UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 
AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


HUMUS  IN  CALIFORNIA  SOILS 


BY 

R.  H.  LOUGHRIDGE 


BULLETIN  No.  242 

Berkeley,   Cal.,   January,    1914 


Printed  at  the  State  Printing  Office,  Friend  Wm.  Richardson,  Superintendent 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT   STATION  STAFF. 

HEADS    OF    DIVISIONS. 

Thomas  Forsyth  Hunt,  Director. 

Eugene  W.  Hilgard,  Agricultural  Chemistry   (Emeritus). 

Edward  J.  Wickson,  Horticulture. 

Herbert  J.  Webber,  Director  Citrus  Experiment  Station ;   Plant  Breeding. 

Hubert  E.  Van  Norman,  Vice-Director. 

William  A.  Setchell,  Botany. 

Myer  E.  Jaffa,  Nutrition. 

Robert  H.  Loughridge,  Soil  Chemistry  and  Physics  (Emeritus). 

Charles  W.  Woodworth,  Entomology. 

Ralph  E.  Smith,  Plant  Pathology. 

J.  Eliot  Coit,  Citriculture. 

John  W.  Gilmore,  Agronomy. 

Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 

Bernard  A.  Etcheverry,  Irrigation. 

Frederic  T.  Bioletti,  Viticulture  and  Enology. 

Warren  T.  Clarke,  Agricultural  Extension. 

John  S.  Burd,  Agricultural  Chemistry. 

Chari.es  B.  Lipman,  Soil  Chemistry  and  Bacteriology. 

Clarence  M.  Haring,  Veterinary  Science  and  Bacteriology. 

Ernest  B.  Babcock,  Genetics. 

Gordon  H.  True,  Animal  Husbandry. 

James  T.  Barrett,  Plant  Pathology,  Citrus  Experiment  Station. 

Burr  B.  Pratt,  Pomology. 

Wm.  G.  Hummel,  Agricultural  Education. 

Frank  L.  Peterson,  Farm  Mechanics. 

David  N.  Morgan,  Assistant  to  the  Director. 

Mrs.  D.  L.  Bunnell,  Librarian. 

DIVISION  OF   SOIL  CHEMISTRY  AND  BACTERIOLOGY. 

Eugene  W.  Hilgard   (Emeritus). 
Robert  H.  Loughridge   (Emeritus). 
Charles  B.  Lipman. 
Leslie  T.  Sharp. 
Paul  S.  Burgess. 
Wm.  F.  Gericke. 


HUMUS  IN  CALIFORNIA  SOILS. 

By  R.   H.  Lougiiridge. 


INTRODUCTION. 
Examinations  of  California  Soils. 

Information  and  data  regarding  the  nature  of  the  soils  of  the  State 
have  been  obtained  through  the  physical  and  chemical  analyses  of 
thousands  of  samples  taken  according  to  our  directions  and  sent  to  our 
laboratory  by  farmers  throughout  California;  by  the  examination  of 
samples  of  a  few  feet  in  depth  taken  by  us  or  other  members  of  the 
station  staff;  and  of  one  hundred  soil  columns  taken  to  depths  of  ten 
or  twelve  feet  from  each  of  the  main  soil  regions  of  the  State,  chiefly  by 
the  author  and  his  assistant,  the  late  P.  E.  Johnson. 

It  has  been  the  policy  of  the  California  Experiment  Station,  from  the 
time  when  Professor  Hilgard  established  it  in  1875  to  the  present  time, 
to  respond  to  the  call  of  farmers  for  information  regarding  problems 
of  the  farm  in  all  of  its  branches,  and  especially  those  of  the  soil  and 
its  products.  The  examination  of  soils  has  been  free  to  the  farmer,  and 
during  these  years  many  thousands  of  samples  of  soil  have  been  sent 
to  us  by  them  to  ascertain  whether  there  be  a  lack  of  plant  food  and 
a  need  of  fertilizers,  whether  alkali  salts  be  present  and  how  gotten  rid 
of,  or  whether  there  be  some  other  causes  of  infertility.  The  samples 
were  for  the  most  part  taken  according  to  our  directions,  and  examined 
as  to  their  physical  properties,  and  as  to  the  approximate  amount  of 
humus,  lime,  and  phosphoric  acid,  and  sometimes  of  potash,  short 
methods  for  these  determinations  having  been  adopted.  Where  alkali 
was  found  to  be  present  in  any  appreciable  amount,  the  percentage  of 
each  salt  was  determined  by  a  regular  analysis. 

These  examinations  of  soils  that  came  from  every  part  of  the  State, 
together  with  such  personal  visits  as  Professor  Hilgard  and  the  author 
were  able  to  make  to  the  main  agricultural  regions,  gave  an  excellent 
insight  into  the  agricultural  conditions  of  every  part  of  the  State  ;  which 
has  been  of  very  great  importance  in  our  work  and  a  special  help 
toward  the  completion  of  a  soil  map  of  the  State,  there  being  no  funds 
available  for  the  prosecution  of  a  soil  survey. 

While  this  work  consumed  much  of  the  time  that  we  would  have 
preferred  to  give  to  research,  we  believe  that  it  has  been  of  value  to 
those  concerned  and  especially  to  the  station,  by  bringing  it  and  the 
farmer  into  close  touch  with  each  other. 

The   Nature  of  Humus  and   its  Formation. 

The  name  humus  should  not  be  applied  to  all  of  the  vegetable  matter 
of  the  soil  in  all  stages  of  decay,  as  many  seem  to  think,  but  only  to  a 
peculiar  product  of  partial  decay  of  vegetable  and  animal  matters 


50  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

brought  about  under  conditions  of  moisture,  warmth,  a  limited  amount 
of  air  and  in  the  presence  of  lime.  Until  humification  of  the  leaves, 
roots  and  other  plant  debris  takes  place  the  beneficial  effects  of  humus 
itself  are  not  obtained,  and  the  material,  while  loosening  the  soil  (some- 
times injuriously),  is  practically  inert  as  far  as  enriching  the  soil  with 
its  nitrogen  and  mineral  elements  is  concerned.  This  was  shown  by  the 
experiments  of  Professor  Hilgard,  carried  on  through  a  period  of  two 
years.     (Soils,  page  359.) 

Humus  contains  all  of  the  decomposition  products  of  both  vegetable 
and  animal  matters,  and  therefore  includes  at  least  minute  quantities  of 
amido,  amin,  and  purin  compounds,  most  of  which  are  beneficial  and 
some  are  injurious  to  vegetation. 

Humus  is  so  thoroughly  disseminated  in  the  soil  that  its  presence  is 
noticeable  only  in  the  dark  color  it  gives  when  in  large  amounts.  It  is 
black  or  brown  in  color,  resembling  charcoal  in  its  lightness  and  porosity 
as  well  as  in  its  destructibility  by  fire.  It  is  colloidal  in  nature  and 
though  derived  from  vegetable  matter,  it  has  lost  all  of  the  fibrous 
and  cellular  structure  of  plants.  It  is  highly  absorbent  of  gases  and  of 
moisture  in  the  latter  case,  swelling  to  eight  to  fourteen  times  its  dry 
volume. 

Humus  has  no  definite  composition  beyond  the  fact  that  it  is  made  up 
of  the  same  elements  that  enter  into  the  composition  of  plants — carbon, 
oxygen,  hydrogen,  nitrogen,  and  some  mineral  elements.  The  propor- 
tion of  carbon  is,  however,  greater  than  in  plants  because  of  the  partial 
decay.  Humus  is  really  a  mixture  of  compounds  in  proportions  that 
vary  with  the  nature  of  the  substance  from  which  it  was  obtained,  and 
from  a  mixture  of  different  substances  in  the  soil.  This  is  especially 
true  with  regard  to  the  nitrogen — the  most  valuable  element  in  humus. 
Some  organic  substances  are  almost  lacking  in  nitrogen  and  yield  a 
humus  containing  but  little  of  it,  while,  on  the  other  hand,  a  humus  may 
be  extremely  rich  in  nitrogen  because  derived  from  substances  very 
rich  in  that  element. 

In  a  soil  humus  is  usually  combined  with  lime  and  other  elements  as 
humates,  and  is  then  not  soluble  in  water,  but  is  dissolved  by  a  solution 
of  caustic  alkali  and  of  carbonate  of  soda,  thus  giving  rise  to  the  name 
"black  alkali."  In  soils  that  are  weak  in  lime  it  often  occurs  as  free 
humic  acid,  and  is  then  soluble  in  water  and  causes  injurious  acidity  in 
soils,  which  must  be  counteracted  by  the  application  of  lime.  By  the 
action  of  air  and  bacteria  it  is  slowly  destroyed  and  carbonic  acid, 
water  and  ammonia  are  produced.  Free  humic  acid  is  frequently  pro- 
duced by  the  growing  of  lime-loving  plants,  such  as  alfalfa  and  other 
legumes,  the  lime  being  absorbed  by  many  successive  crops  and  the 
humus  left  behind  as  humic  acid.  This  has  taken  place  in  the  Eel  River 
Valley  soils  of  Humboldt  County,  California,  and  only  the  application 
of  lime  has  restored  the  land  to  its  former  fertility. 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  51 

Amount  of  Humus  Formed  from  Vegetable  Matter.  With  regard  to 
the  amount  of  humus  formed  from  the  decay  of  vegetable  matter,  Pro- 
fessor Hilgard  says  (Soils,  page  128)  :  "Only  very  general  and  indefi- 
nite estimates  can  be  given  of  the  amount  of  humus  formed  from  a 
given  amount  of  vegetable  matter,  since  these  must  vary  according  to 
the  conditions  under  which  the  transformation  occurs.  The  greater  or 
less  access  of  air  and  of  moisture,  the  temperature  and  pressure  under 
which  the  process  occurs,  will  modify  very  materially  the  quantitative 
as  well  as  the  qualitative  result.  In  the  hot,  arid  regions  the  fallen 
leaves  may  wholly  disappear  by  oxidation  on  the  surface  of  the  ground, 
while  under  humid  conditions  they  are  mostly  incorporated  with  the 
surface  soil.  If  we  assume  that  in  the  humification  of  plant  debris 
no  nitrogen  is  lost,  it  would  seem  that  in  the  humid  region  one  part  of 
normal  soil  humus  might  be  formed  from  five  to  six  parts  of  dry  plant 
debris ;  while  in  the  extreme  regime  of  the  arid  regions  from  eighteen  to 
twenty  parts  of  the  same  would  be  required.  But  as  most  probably 
some  nitrogen  is  lost  in  the  process  of  humification,  a  considerably  larger 
proportion  of  original  substance  may  be  actually  required." 

Professor  Snyder  of  the  Minnesota  Experiment  Station  by  his  experi- 
ments (Bulletin  53)  obtained  the  following  results:  One  part  of  humus 
to  32.7  parts  of  fresh  cow  manure,  or  24.5  parts  of  green  clover,  or  10.8 
of  meat  scraps;  the  humus  of  the  cow  manure  contained  6.16  per  cent 
of  nitrogen,  that  of  the  clover  8.24  per  cent  and  that  of  meat  scraps 
10.96  per  cent.  Oat  straw  and  sawdust  remained  in  the  ground  appar- 
ently unchanged  for  more  than  a  year,  but  finally  gave  one  part  of 
humus  for  5.5  parts  of  straw  and  for  9.5  of  sawdust,  respectively;  the 
humus  of  the  straw  had  2.5  per  cent  of  nitrogen  and  that  of  the  saw- 
dust only  0.3  per  cent.  In  the  drier  soils  of  California  the  straw  and 
sawdust  would  doubtless  remain  unchanged  for  several  years. 

Value  of  Humus. 

The  great  value  of  humus  to  the  soils  of  this  State  is  not  as  well 
recognized  generally  by  farmers  as  it  should  be,  and  they  probably  do 
not  fully  realize  that  by  maintaining  a  proper  supply  in  the  soil  through 
a  careful  system  of  green-manuring  they  will  avoid  the  expense  of 
hundreds  of  dollars  worth  of  nitrogen,  that  most  expensive  of  fertilizers, 
and  at  the  same  time  keep  the  soil  in  a  splendid  physical  condition  not 
produced  by  fertilizers  alone. 

Potash,  phosphoric  acid  and  nitrogen  have  their  beneficial  effect  only 
in  maintaining  the  growth  and  productiveness  of  plants  and  do  not 
affect  the  soil  itself  materially ;  lime  influences  the  structural  formation 
of  the  plant,  the  character  of  the  fruit,  the  physical  condition  of  soils, 
and  neutralizes  any  acid  condition.  But  humus  goes  still  farther  by 
not  only  supplying  important  and  expensive  elements  of  food  to  the 


52  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

plant  and  producing  excellent  mechanical  conditions  in  the  soil,  but  by 
influencing  the  life  and  activity  of  important  bacteria.  The  following 
is  a  brief  summary  of  the  value  oi  humus : 

Humus  Improves  the  "nmlstre  of  Soils.  It  does  this  in  clay  soils  by 
causing  aggregation  or  flocculation  of  the  particles  of  clay  into  a  granu- 
lar condition,  thus  producing  looseness  and  easier  tillage.  The  soil  is 
thus  better  aerated  and  ventilated,  and  is  made  warmer  for  plant 
development.  By  this  condition  it  is  made  more  receptive  for  rain- 
fall, permits  greater  freedom  in  the  downward  percolation  of  water,  and 
prevents  its  evaporation  by  the  sun's  heat.  "When  incorporated  with 
loose  sandy  soils  it  occupies  the  spaces  between  the  grains,  thus  binding 
the  sand  together,  and  giving  better  texture.  By  this  the  soil  is  made 
to  hold  moisture  which  would  otherwise  be  lost  by  percolation  and  by 
evaporation ;  and  it  is  made  cooler  in  summer  because  of  absorption  and 
radiation  of  the  heat  from  the  black  particles.  It  decreases  the  conduc- 
tivity of  a  sandy  soil  for  heat,  thus  preventing  overheating  of  surface 
plant  roots  in  such  soils. 

Humus  Largely  Prevents  the  Crusting  of  Soil  Surfaces.  One  of  the 
troubles  that  California  farmers  have  to  contend  with  is  the  tendency 
of  the  soil  to  become  crusted  over  or  compacted  after  a  rainfall  or  after 
irrigation.  This  seems  to  be  quite  general  throughout  the  State,  and 
we  believe  is  in  part  due  to  insufficiency  of  humus  and  of  other  vegetable 
matter  which  would  maintain  a  granular  structure  in  the  soil.  An 
intermixture  of  well -rotted  stable  or  farmyard  manure  would  also  tend 
to  prevent  the  crusting,  but  the  turning  under  and  humifi cation  of 
suitable  green-manure  crops  until  the  amount  of  humus  produced 
reached  several  per  cent  would  be  better  and  more  permanent. 

Humus  in  the  Soil  Absorbs  Water  and  Water  Vapor.  This  is  due  to 
its  porosity,  which  gives  to  it  a  very  high  absorptive  power.  But  it  does 
this  only  in  its  diffused  colloidal  condition  in  the  soil.  When  separated 
from  the  soil  and  dried  at  a  low  temperature  it  loses  its  colloidal  nature 
and  acts  only  as  so  much  fine  silt. 

Humus  Promotes  Chemical  Action  in  the  Soil.  The  humus  acts  upon 
the  inert  and  insoluble  minerals  in  the  soil  and  slowly  renders  their 
elements  of  plant-food  available  for  plant  use. 

According  to  Prof.  Harry  Snyder  of  Minnesota,*  it  is  only  the  humus 
that  contains  a  high  percentage  of  nitrogen  that  acts  most  energetically 
upon  the  inert  mineral  matter,  and  he  designates  this  as  "active 
humus,"  while  that  with  low  content  of  nitrogen  he  classes  as  "inac- 
tive humus." 

Humus  Contains  Nitrogen  and  is  a  Nitrogen  Fertilizer.  Nitrogen 
exists  in  the  soil  partly  in  the  free  state  in  the  air  that  permeates  the 
soil  mass;  partly  in  the  vegetable  and  animal  material  that  has  not 


■See  Chemistry  of  Soils  and  Fertilizers,  page  100. 


Bulletin  242]  HUMUS   IN    CALIFORNIA    SOILS.  53 

undergone  humification ;  partly  in  the  humified  vegetable  and  animal 
matter  in  water,  and  hence  very  variable  in  amount  from  day  to  day 
and  liable  to  be  lost  by  drainage.  That  the  unhumified  material  in  the 
soil  does  not  yield  its  nitrogen  to  plants  until  after  complete  humifica- 
tion has  been  shown  by  the  experiments  of  Professor  Hilgard,  whose 
conclusions  are  as  follows :  ' '  It  thus  appears  that  although  the  nitrogen 
of  the  unhumified  organic  matter  constituted  about  40  per  cent  of  the 
total  in  the  original  soil,  it  would  during  the  entire  year  have  con- 
tributed only  to  an  insignificant  extent  to  the  available  nitrate  supply ; 
while  the  fully  humified  'matiere  noire'  contributed  fourteen  times  as 
much.  During  the  growing  season  of  four  or  five  months  the  unhumi- 
fied organic  matter  would  have  yielded  practically  nothing  to  the  crop." 
(Soils,  page  360.) 

The  humus  itself  then  is  the  most  reliable  source  of  nitrogen,  keeping 
it  in  reserve,  to  be  given  to  the  roots  of  plants  by  degrees,  by  ammonify- 
ing and  nitrifying  bacteria  and  at  the  same  time  when  most  needed, 
viz,  in  the  growing  season.  The  fertilizing  value  of  humus  depends,  as 
has  already  been  remarked,  upon  the  amount  of  nitrogen  that  it  contains 
and  which  may  be  changed  to  ammonia  and  nitrates  through  the  agency 
of  bacteria  and  given  to  the  soil  and  plant.  The  nitrogen  content 
naturally  varies  according  to  the  nature  of  the  materials  from  which  the 
humus  was  formed  and  to  any  diminution  that  may  have  occurred  from 
bacterial  action  or  other  causes,  and  we  therefore  find  great  differences 
in  one  and  the  same  column  of  soil.  Sometimes  the  difference  is  very 
great  between  one  foot  and  the  next  below,  for  which  it  is  difficult  to 
account. 

This  humus  nitrogen  is  not,  so  far  as  we  know,  directly  available  to 
plants,  except  in  minute  quantities  of  soluble  amido  compounds  formed 
by  the  decay  of  nitrogenous  matter,  but  becomes  so  through  the  action 
of  ammonifying  and  nitrifying  bacteria  in  the  soil,  which  convert  it 
into  nitrates. 

The  humus,  therefore,  is  a  valuable  source  of  nitrogen  for  plant  use, 
and  at  the  same  time  is  a  cheap  source,  because  a  crop  of  legumes  can 
be  grown  at  but  the  small  expense  of  growing,  cutting,  and  plowing 
under.  The  percentage  of  nitrogen  that  humus  contains  varies  in  Cali- 
fornia from  a  little  more  than  one  per  cent  in  the  desert  sagebrush  lands 
to  as  much  as  twenty  per  cent  in  better  lands;  the  average  is  from 
five  to  six  per  cent. 

Humus  Contains  Soluble  Mineral  Plant-food.  When  humus  is  sepa- 
rated from  the  soil  and  burned  it  leaves  an  ash  which  contains  large 
percentages  of  potash,  soda,  phosphoric  acid  and  lime,  which  while  in 
combination  with  humus  are  regarded  as  being  immediately  available 
for  plant  use.     While  the  amount  thus  contained  in  the  soil  is  not  large, 


54  UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 

varying  from  .01  to  .05  per  cent  of  potash  and  of  phosphoric  acid,  it 
adds  very  materially  to  the  fertility  of  the  soil,  the  latter  percentage 
being  equivalent  to  about  two  thousand  pounds  per  acre-foot. 

Destruction  of   Humus. 

Humus,  like  all  other  organic  substances,  may  be  destroyed  by  dry 
decay  through  exposure  to  hot  dry  air,  either  in  the  immediate  surface 
of  the  soil  or  in  the  portion  that  is  stirred  by  the  plow  or  cultivator. 
The  loss  each  year  is  imperceptible  and  the  effect  is  seen  only  after 
many  years  of  cultivation,  except  in  soils  naturally  weak  in  humus, 
when  there  is  a  decrease  in  productiveness  and  a  tendency  to  form  a 
hard  crust  on  the  surface.  In  Minnesota*  it  was  found  that  cultivation 
of  wheat  for  eight  years  caused  a  loss  of  17,000  pounds  of  humus  and 
1,700  pounds  of  nitrogen  per  acre.  The  crop  itself  used  350  pounds 
of  the  nitrogen,  thus  leaving  1,350  as  the  loss  due  to  destruction  of  the 
humus  by  cultivation.  It  was  also  found  that  summer-fallow  was  more 
destructive  of  humus  and  its  nitrogen  than  was  continuous  cultivation 
in  grain;  the  loss  in  two  years  by  summer-fallow  was  600  pounds  of 
nitrogen  or  twice  the  amount  used  for  two  crops  of  wheat. 

Humus  in  California  Soils. 

In  California  the  general  practice  of  continuous  grain-growing  on 
the  same  land,  and  especially  of  summer-fallow,  for  the  past  many  years 
has  resulted  in  the  lessening  of  the  humus  content  and  its  nitrogen  in 
the  soil  by  the  cultivation  required,  and  as  a  consequence  the  yields  of 
grain  have  fallen  off  year  by  year.  An  instance  of  this  destruction  by 
cultivation  was  shown  in  the  examination  of  the  soil  of  the  University 
Farm  at  Davis,  which  had  been  under  continuous  grain  culture  for 
thirty  or  more  years  when  purchased  by  the  University.  The  humus 
percentage  of  the  first  foot  was  found  to  be  .79,  with  4.55  per  cent  of 
nitrogen.  The  humus  in  the  virgin  soil  just  outside  of  the  wheat  field 
was  1.25  per  cent  and  its  nitrogen  5.90  per  cent.  This  difference  of 
.46  per  cent  of  humus  and  1.35  per  cent  of  nitrogen,  between  the  culti- 
vated and  uncultivated  soils,  indicates  a  loss  of  more  than  one  third 
of  the  nitrogen,  caused  by  wheat  culture.  This  is  equivalent  to  18,400 
pounds  of  humus  and  1,520  pounds  of  nitrogen  per  acre.  The  effect 
of  this  loss  of  humus  and  its  nitrogen  has  been  seen  in  the  falling 
off  in  productiveness  and  in  an  increased  tendency  of  the  soil  to  form 
a  thin  surface  crust,  and  in  other  ways  to  so  affect  the  physical  prop- 
erties of  the  soil  as  to  interfere  with  the  proper  development  and 
functions  of  the  grain  roots.  The  soil  becomes  lighter  in  color,  more 
compact,  poorly  aerated  and  less  retentive  of  moisture.  Percolation  of 
water  from  rainfall  or  irrigation  is  slower  and  evaporation  from  the 
surface  more  rapid,  the  soil  becoming  dry  to  quite  a  depth. 

This  loss  of  humus  and  its  nitrogen  in  the  surface  soil  is  a  necessary 


♦Bulletin  No.   70,  Minn.  Expt.  Station. 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  55 

evil  everywhere,  for  the  soil  must  be  plowed  and  cultivated  to  maintain 
proper  conditions  for  high  productiveness,  and  it  is  a  loss  more  quickly 
felt,  of  course,  in  soils  where  the  amount  of  humus  is  low.  After  many 
years  of  cultivation  it  will  be  felt  in  soils  having  a  good  supply  of  humus, 
but  which  exists  only  in  the  upper  six  or  eight  inches.  It  should  not 
be  felt  in  decreased  productiveness  of  the  crop  for  fifty  or  one  hundred 
years  in  soils  having  a  good  humus  content  through  a  depth  of  several 
feet :  and  it  would  not  be  if  proper  attention  were  paid  to  the  mainte- 
nance of  good  tilth,  aeration  and  water  supply,  and  to  the  encourage- 
ment of  the  penetration  of  the  roots  to  the  deep  source  of  supply.  Had 
California  grain-growers  treated  their  soils  rightly  during  the  past 
years  and  kept  them  in  good  tilth  to  a  depth  of  10  or  12  inches,  the  high 
yield  of  40  to  50  bushels  of  wheat  in  early  years  (e.  g.,  on  the  sandy 
lands  of  Stanislaus  County  in  1879)  would  have  been  maintained  to 
the  present  time,  for  the  grain  roots  would  have  found  ample  supplies 
of  nitrogen  in  the  humus  which  we  show  in  this  bulletin  exists  to  a 
depth  of  many  feet.  The  loss  of  humus  has,  however,  been  severely  felt 
in  the  soils  of  many  parts  of  the  State,  not  only  because  there  was  natu- 
rally but  a  small  amount  in  the  surface  soil,  but  largely  because  of  the 
methods  of  cultivation  and  treatment  the  soil  has  received.  In  fact,  this 
shallow  plowing  seems  to  be  the  source  of  most  of  the  trouble  that  comes 
to  the  farm  and  orchard  in  a  country  so  blessed  with  deep  and  rich  soils. 

Humus  in  the  Surface  Foot. 

The  results  of  the  soil  examinations  have  brought  out  the  fact  that, 
while  the  supply  of  potash  is  as  a  rule  very  large  and  should  not  need 
replenishment  by  fertilizers  for  decades,  and  that  phosphoric  acid  is 
generally  fair  in  amount,  except  in  lands  that  have  been  in  wheat 
culture  for  many  years,  the  percentage  of  humus  in  all  surface  soils 
except  tule  swamps  is  quite  low  and  has  required  a  system  of  green 
manuring  to  bring  the  land  back  into  the  best  condition. 

Cursory  Examinations.  Because  of  the  time  required  to  make  an 
accurate  analysis  of  each  soil  and  especially  as  the  question  was  chiefly 
as  to  the  sufficiency  or  insufficiency  of  potash,  phosphoric  acid,  lime,  and 
humus,  we  adopted  at  the  beginning  a  scale  of  tests  by  which  approxi- 
mate results  could  be  reached  very  quickly.  The  results  for  humus 
were  graded  into  "good"  for  1  per  cent  and  above,  "fair"  for  0.7  to 
1  per  cent  and  "poor"  for  less  than  .7  per  cent  in  the  surface  soil.  It 
may  be  of  interest  to  give  a  summary  of  the  results  obtained  from  1893 
to  1908,  the  time  when,  because  of  pressure  of  more  important  work, 
these  examinations  were  brought  to  a  close. 

The  following  table  presents  the  results,  by  agricultural  regions,  from 
1,456  soils  in  which  the  humus  was  determined.  The  percentages  of 
"good"  for  those  above  1  per  cent,  "fair"  from  .75  to  1  per  cent,  and 


56 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


"poor"  for  less  than  .75  per  cent  of  humus  are  given  for  each  region, 
and  also  for  the  entire  State. 


Number 

of  soils 

examined 

Good  humus 

Fair  humus 

Poor  humus 

Sacramento  Valley  __  _      _  ___. 

211 
434 
66 
398 
347 

Per  cent 
55 
24 
59 
64 
43 

Per  cent 

18 
24 
12 
19 
23 

Per  cent 
27 

San  Joaquin  Valley _             

52 

Foothills  of  Sierra  Nevada  _ 

29 

Coast  Range  valleys.-. 

17 

Southern  California  

34 

Average    _ 

1,456 

46 

21 

33 

It  will  be  seen  from  the  above  that  more  than  one  half  of  the  soils  of 
the  Sacramento,  Foothill,  and  Coast  Range  regions  that  were  sent  for 
examination  by  farmers  of  those  regions  had  as  much  as  one  per  cent  of 
humus,  though  for  the  State  at  large,  only  46  per  cent  of  the  1,456  soils 
had  that  amount. 

Regular  Analyses  of  Carefully  Selected  Soils.  From  time  to  time, 
since  the  establishment  of  the  station,  nearly  five  hundred  complete 
analyses  have  been  made  of  soils  chosen  to  represent  the  different  agri- 
cultural regions  and  conditions  in  the  State,  and  among  the  determina- 
tions was  that  of  the  exact  amount  of  humus  in  the  surface  soil.  The 
method  of  humus  determination  used  was  what  is  known  as  the 
Grandeau  Method  as  modified  by  Professor  Hilgard.  The  results  there- 
fore more  nearly  represent  actual  average  conditions  in  the  soils  of  Cali- 
fornia. The  following  table  shows  the  average  percentages  of  humus  in 
the  soils  of  the  several  regions. 

Table  Showing  Percentages  of  Humus  in  Surface  Soils. 


Regions 


Number  of 
soils  exam- 
ined for 
humus 


Average  per- 
centage of 
humus 


Percentage  of 

soils  having 

more  than 

1  per  cent 

of  humus 


Tules  and  Meadows 

Coast  Range  valleys 

Sierra   Foothills   

Sacramento  Valley  

Southern  California  

San  Joaquin  Valley 

Desert  plains  and  Lava-bed  valleys 

General  average  for  State 


14 
91 
46 
29 

61 
67 

•2:\ 


3.62 

1.69 

1.23 

1.14 

.94 

.79 

.51 


all 
67 
41 
50 
28 
29 
0 


331 


1.25 


40 


The  general  average  of  humus  in  the  331  surface  soils  taken  from 
different  parts  of  California,  and  supposed  to  fairly  represent  all  of 
the  agricultural  regions,  is  1.25  per  cent.  If,  however,  the  tule  marshes 
and  the  meadow  lands  are  omitted  from  the  calculation,  then  we  find 
that  the  general  humus  percentage  is  1.15.  This  is  almost  the  identical 
humus  percentage  of  the  average  of  306  soils  of  the  arid  region  (1.13) 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  57 

given  by  Professor  Hilgard  in  his  book  on  Soils,  page  377,  and  embrac- 
ing soils  from  Idaho,  Arizona,  Oregon,  and  California. 

It  is  a  peculiar  fact  that  of  the  331  soils  examined  only  forty  per  cent 
had  more  than  one  per  cent  of  humus  in  the  first  foot,  thus  showing  the 
need  for  replenishment  by  the  turning  under  and  humification  of  green 
manure  crops  for  a  series  of  years. 


58  UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION. 


DISTRIBUTION  OF  HUMUS  DOWNWARD  FOR  MANY 
FEET  IN  CALIFORNIA  SOILS. 


A  very  marked  characteristic  of  the  soils  of  California  is  their  great 
depth,  as  exemplified  in  the  uniformity  of  color  through  a  depth  of 
several  feet,  their  good  texture  affording  easy  penetration  of  plant  roots 
often  to  depths  of  twenty  and  even  sixty  feet  below  the  surface; 
abundant  food  available  for  plant  use  throughout  these  depths,  an 
absence  of  any  well  defined  subsoil  except  at  a  depth  of  several  feet 
below  the  surface,  the  absence  of  any  compact  clay  substratum  differing 
from  the  surface  foot,  and  the  presence  of  humus  to  as  much  as  ten  or 
more  feet.  In  each  of  these  particulars  the  soils  of  this  State  differ 
from  those  of  the  humid  states  east  of  the  Rocky  Mountains,  and 
because  of  this  the  methods  of  culture  are  different,  and  in  the  applica- 
tions of  fertilizers  to  the  soil  it  is  only  with  difficulty  that  they  can  be 
made  to  reach  the  feeding  roots  of  plants. 

These  facts  are  soon  realized  by  farmers  from  the  East  who  come  to 
the  farms  of  California,  and  find  that  the  eastern  methods  of  cultivation 
will  not  give  the  best  results,  and  must  be  changed  to  those  found  to  be 
more  successful.  There  are  several  striking  facts  regarding  the  humus 
itself  in  the  soils  of  California  that  deserve  mention  and  which  dis- 
tinguish them  from  the  soils  of  the  humid  region  of  the  eastern  states, 
one  of  which  has  but  recently  been  brought  out  in  the  examinations 
that  are  being  made  of  the  many  typical  twelve-foot  columns  from  the 
chief  agricultural  divisions  of  the  State.  These  facts  are:  First,  the 
small  amount  of  humus  in  the  first  foot  of  all  soils,  in  comparison  with 
three  or  more  times  as  much  in  eastern  soils;  second,  the  distribution 
of  the  humus  downward  to  depths  of  twelve  and  more  feet  in  upland 
soils,  the  total  of  which  is  greater  than  that  of  the  eastern  soils;  and 
third,  the  rather  higher  percentage  of  humus  nitrogen  in  the  upper 
feet  and  the  distribution  of  the  humus  nitrogen  throughout  the  twelve 
feet,  thus  giving  the  soils  of  the  arid  region  a  higher  total  of  humus- 
nitrogen  content  than  is  found  in  the  humid  soils. 

Bacterial  Activity  in  the  Soil.  Another  highly  important  advantage 
possessed  by  California  in  her  soils  is  the  fact  recently  brought  out  by 
Prof.  C.  B.  Lipman  of  this  station  in  his  paper  on  the  Distribution  and 
Activities  of  Bacteria  in  Soils  of  the  Arid  Region* :  ' '  that  soils  of  the 
arid  region  at  all  depths  studied  show  ammonifying  powers,  which  are, 
however,  generally  most  vigorous  in  the  first  six  or  eight  feet.  In  one 
case  ammonification  was  noted  in  soil  from  a  depth  of  fifteen  feet,  or 
adjoining  the  watertable  *  *  *  As  for  nitrification  my  data  pre- 
sent again  features  of  striking  interest.     They  go  to  prove  that  nitrate 


*Univ.   of  California   Publications,   Agricultural   Sciences,   Vol.    I,   No.    1. 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  59 

formation,  like  ammonification,  goes  on  at  much  greater  depths  in  soils 
of  the  arid  than  in  soils  of  the  humid  region  #  *  *  That  nitrifica- 
tion is  found  commonly  down  to  a  depth  of  five  or  six  feet  in  soils  of  the 
arid  region.  In  one  case  a  soil  from  an  eight-foot  depth  showed  a  vig- 
orous nitrifying  power." 

Professor  Lipman's  observations  greatly  emphasize  the  importance  of 
having  the  roots  of  the  various  crops  utilize  the  food  supplies  at  their 
command  at  depth  of  many  feet;  for  not  only  is  there  a  nitrogen 
supply,  but  our  investigations  on  the  soil  columns  show  that  the  amount 
of  available  phosphoric  acid  and  of  potash  is  large  at  depths  of  twelve 
and  more  feet. 

Leveling  of  Lands.  The  existence  of  humus  and  an  abundance  of 
available  plant  food  at  depths  of  many  feet  in  our  soils  is  well  and 
practically  demonstrated  by  the  fact  that  when  lands  are  leveled  and 
hogwallows  (except  in  an  alkali  country)  filled  up  by  cutting  down  the 
hii locks  of  several  feet  height,  the  exposed  undersoil  is  fully  as  pro- 
ductive and  as  quickly  capable  of  producing  good  crops  as  the  original 
surface  soil.  This  leveling  is  very  generally  and  successfully  practiced 
in  California,  and  especially  in  the  reddish  hogwallow  lands  of  the 
eastern  side  of  the  San  Joaquin  Valley,  before  planting  orchard  trees. 
The  rock-like  hardpan  in  the  bottom  of  the  hogwallows  at  a  depth  of  a 
few  feet  is  broken  up  by  a  small  charge  of  dynamite  to  afford  good 
drainage,  and  the  hillocks  cut  down  by  plowing  and  scraping  their  soils 
into  the  natural  depressions.  There  is  no  unproductive  or  raw  clay  sub- 
stratum similar  to  that  of  humid  climates  to  be  cut  into  and  exposed, 
and  which  must  remain  for  many  months  before  being  sufficiently  acted 
upon  by  weathering  agencies  to  yield  even  a  growth  of  grass. 

Obtaining  Soil  Columns.  In  1883  we  were  asked  by  the  California 
Commission  to  furnish  a  few  typical  soils  of  the  State  for  the  state 
exhibit  at  the  St.  Louis  Exposition,  and  it  was  decided  to  make  this 
feature  of  depth  a  prominent  one  by  securing  soil  columns  of  about 
twelve  feet  in  depth,  each  foot  in  the  column  being  shown  in  its  place  in 
wide  bottles  placed  one  above  the  other  and  properly  labeled.  Eighteen 
of  these  columns  were  taken  by  us  from  different  sections  of  the  State 
and  placed  on  exhibition.  These  proved  to  be  so  attractive  to  visitors 
by  illustrating  the  nature  and  depth  of  California  soils  and  their  exam- 
ination proved  of  such  importance  in  establishing  the  presence  of  avail- 
able plant  food  and  of  humus  at  great  depths  that  we  have  added  to 
the  collection,  and  there  are  now  one  hundred  and  ten  columns  which 

Note. — Much  difficulty  was  experienced  at  the  outset  in  securing  soils  to  a  depth 
of  twelve  feet  without  great  expenditure  of  time  and  money,  as  large  samples  of 
a  foot  each  were  necessary  for  representatives  in  the  soil  column  and  for  analyses. 
A  posthole  auger  (made  and  patented  by  Messrs.  Iwan  Bros.,  of  South  Bend, 
Indiana)  was  at  last  found  and  proved  to  be  admirably  suited  to  the  purpose;  it 
cuts  rapidly  on  bottom  and  sides  and  holds  the  soil  well.  Pitted  with  extension 
pipes  of  three  foot  lengths  which  are  easily  removable,  the  auger  is  made  to  reach 
any  depth  except  when  coarse  gravel  or  hardpan  is  encountered. 


60  UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 

represent  the  most  important  of  the  soils  of  the  many  agricultural 
regions  of  the  State.  These  have  been  arranged  in  vertical  positions 
in  the  soil  museum  of  Budd  Hall  and  are  being  examined  as  rapidly  as 
possible  from  a  chemical,  physical,  and  biological  standpoint.  The 
results  will  be  presented  in  a  special  report. 

Distribution    of    Humus    in    Soil    Columns    from    Each    Agricultural    Region. 

The  agricultural  regions  of  the  State  comprise  the  Sacramento  and 
San  Joaquin  valleys,  forming  together  the  central  Great  Valley,  the 
Foothills  lying  on  the  western  slope  of  the  Sierra  Nevada,  the  many 
Coast  Range  valleys  and  low  hills  among  the  mountain  ranges  along  the 
western  side  of  the  State,  the  Southern  California  valleys  and  the  low 
hills,  the  Desert  Plain  which  is  being  brought  under  cultivation  by  the 
development  and  use  of  irrigation  water,  and  the  Northeastern  Lava- 
bed  valleys.  A  large  portion  of  the  State  is  too  mountainous  and 
rugged  for  tillage  and  is  partly  timbered  with  forests  of  redwood,  pine, 
and  other  trees  suitable  for  lumber.  The  redwood  forests  form  a  region 
of  the  Coast  Range  of  mountains. 

As  the  object  of  this  investigation  was  chiefly  to  ascertain  the  extent 
to  which  humus  was  found  in  the  lower  depths  of  the  soils,  the  soil 
columns  were  only  taken  from  those  regions  whose  soils  are  many 
feet  in  depth.  The  number  of  columns  obtained  was  110  from  thirty- 
seven  counties,  each  column  intended  to  represent  a  characteristic  type 
of  land  in  its  particular  region.  There  are  of  course  very  many  small 
valleys  and  minor  soil  regions  that  have  not  been  included  in  this 
investigation,  some  of  which  may  be  taken  up  later  and  reported  when 
the  results  of  the  chemical  and  physical  examination  of  these  soil 
columns  are  given  to  the  press.  The  analyses  of  the  first  foot  of  the  soils 
of  many  of  these  regions  have  already  been  published  in  the  reports  of 
this  station.  It  is  believed  that  the  results  presented  in  this  investiga- 
tion represent  very  well  the  humus  conditions  that  prevail  in  the  soils 
in  general  throughout  the  State. 

The  humus  and  nitrogen  determinations  given  in  the  following  pages 
were  made  successively  by  Messrs.  F.  E.  Johnson,  M.  E.  Holter,  and 
F.  H.  "Wilson. 

Soil   Columns  of  the  Sacramento   Valley. 

The  valley  of  the  Sacramento  River,  lying  between  the  two  great 
mountain  ranges — Sierra  Nevada  on  the  east  and  Coast  Range  on  the 
west — and  which  unite  on  the  north,  covers  an  area  of  6,200  square 
miles.  The  valley  is  widest  on  the  south  where  it  unites  with  the  San 
Joaquin  Valley.  Within  its  area  are  four  or  five  general  and  highly 
distinct  soil  regions,  or  types,  each  of  which  is  represented  by  one  or 
more  soil  columns  in  our  collection,  or  eighteen  in  all. 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  61 

Alluvial  Lands.  These  border  the  Sacramento  River  and  are  tim- 
bered with  sycamore,  white  oak,  and  ash.  The  soil  is  a  dark  loam  with 
little  or  no  change  to  the  depth  of  twelve  feet,  as  shown  in  the  soil 
columns,  and  even  deeper.  Three  columns  were  taken  from  the  follow- 
ing localities:  Near  Cottonwood,  Shasta  County,  by  W.  S.  Guilford; 
Glenn  post  office,  in  Glenn  County,  east  of  Willows ;  and  near  Perkins, 
Sacramento  County,  by  Professor  George  Roberts,  now  of  the  Kentucky 
Agricultural  College.  To  these  was  added  a  column  of  the  alluvium  of 
Chico  Creek,  taken  from  the  Bidwell  place,  at  Chico,  Butte  County. 

Clay  Loams  of  the  Valley.  These  reach  south  from  near  Red  Bluff 
and  occupy  the  central  part  of  the  Sacramento  Valley.  As  typical  of 
this  class  of  soils,  seven  columns  were  obtained  from  the  following 
localities:  Three  miles  west  of  Tehama,  Tehama  County;  Willows, 
Glenn  County;  J.  W.  Walton's  place  a  few  miles  south  of  Yuba  City, 
Sutter  County;  Woodland,  Yolo  County;  the  University  Farm,  Davis, 
Yolo  County;  Live  Oak,  Sutter  County,  and  from  near  Elmira,  Solano 
County.  In  each  case  a  depth  of  12  feet  was  reached  except  at  Live 
Oak,  where  at  9  feet  the  presence  of  water  prevented  a  deeper  sampling. 

Black  Adobe  Clay  Soils.  There  are  several  regions  of  these  black 
clays  within  the  eastern,  western,  and  southern  parts  of  the  Sacra- 
mento Valley.  One  of  these  reaches  from  southwest  of  Yuba  City 
northward,  passing  west  of  Gridley  and  beyond  Biggs.  A  column  was 
taken  from  this  belt,  a  few  miles  southwest  of  Yuba  City,  the  surface 
soil  of  which  contained  39  per  cent  of  clay.  Below  this  upper  foot  the 
color  changed  from  black  to  gray.  Another  column  was  taken  by  F.  E. 
Johnson  from  near  Biggs.  This  contained  50  per  cent  of  clay  in  its 
upper  foot  and  the  black  color  changed  to  gray  below  the  third  foot. 

A  region  of  black  clay  lies  three  miles  east  of  Willows,  Glenn  County, 
whose  surface  foot  contains  47.46  per  cent  clay,  and  the  black  color 
extends  through  five  feet.  A  column  of  this  was  taken  to  the  depth  of 
twelve  feet.  Another  column  was  taken  from  a  body  of  intensely 
clayey  and  black  land  lying  south  of  Dixon.  It  contains  61.75  per  cent 
of  clay. 

Red  Mesa  and  "Bedrock  Lands."  These  form  a  wide  border  along 
the  eastern  and  northern  sides  of  the  valley,  and  are  characterized  by 
usually  shallow  soils  underlaid  by  either  heavy  compact  red  clays,  or 
by  cemented  beds  of  gravel  and  grit,  forming  a  hardpan  or  bedrock  at 
depths  of  from  two  to  five  feet  below  the  surface.  Because  of  the 
shallowness  of  these  lands,  this  region  is  represented  by  but  three 
columns;  one  from  near  Sheridan,  Placer  County,  representing  the 
lands  on  the  eastern  side  of  the  valley;  another  from  the  bluff  of  Oak 
Creek,  southwest  from  Red  Bluff,  and  one  half  mile  west  of  the  Corn- 
ing road;  and  still  another  taken  by  F.  E.  Johnson  near  Acampo,  San 
Joaquin  County. 
2— bul242 


62  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 

Humus  and  Humus-nitrogen  in  Soils  of  the  Sacramento  Valley. 


Per  cent  humus 

Per  cent  humus- 
nitrogen  in  soil 

First 
foot 

Upper  3  feet 

Twelve  feet 

First 
foot 

Average 
per  foot 

Sum  of 

per  cents 

Average 
per  foot 

Sum  of 
per  cents 

Upper 
3  feet 

Alluvial   soils  — . 

1.47 
1.16 

.95 
.47 

.92 
.73 

.77 
.30 

1.47 

2.20 

2.39 

.90 

.67 
.31 
.42 
.15 

7.50 
3.62 
5.02 
1.43 

.08 
.06 
.05 
.03 

.06 

Black  clay  adobe 

.04 

Gray  clay  loams  _  _  _  _ 

.05 

Red  mesa  lands -    . 

.02 

It  would  naturally  be  supposed  that  because  of  their  deep  color  the 
black  clay  adobe  soils  would  contain  more  humus  than  any  other  soil, 
but  the  above  results  show  that  such  is  not  the  case,  for  the  alluvial  soils 
are  richer,  and  even  the  gray  loams  have  nearly  as  much  as  the  black 
adobe  in  the  first  foot  and  are  a  little  richer  in  the  rest  of  the  column. 

The  color  of  a  soil,  then,  is  no  certain  guide  as  to  the  relative  amount 
of  humus  it  contains. 

Among  the  individual  columns  the  richest  of  the  alluvial  group  are 
those  from  Glenn  and  Chico,  the  former  in  the  upper  three  feet  and 
the  latter  in  the  entire  column ;  there  is  .52  per  cent  in  the  twelfth  foot 
of  the  Chico  column. 

The  richest  of  the  clay  loam  group  is  that  from  Davis,  the  average  in 
the  upper  three  feet  being  1.16  per  cent  and  an  average  of  .755  for  the 
entire  column;  the  twelfth  foot  contains  .69  per  cent.  The  columns 
from  Tehama,  Waltons,  and  Willows  are  next  in  their  respective  per- 
centages, Waltons  being  the  richest  in  the  upper  three  feet. 

The  black  adobe  east  of  Willows  is  the  richest  of  the  four  that  form 
the  composite  column,  and  contains  an  average  of  1.27  per  cent  in  the 
upper  three  feet. 

Soil   Columns  of  the  San   Joaquin   Valley. 

San  Joaquin  Valley,  with  an  area  of  one  thousand  square  miles, 
possesses  many  large  and  distinct  soil  types  or  regions,  each  of  which 
is  represented  in  our  soil  collection  in  columns  of  ten  or  twelve  feet 
each. 

Twenty-four  localities  in  eight  counties  were  selected  from  which  to 
obtain  columns  of  soil  as  nearly  typical  as  possible  of  each  region,  and 
fifteen  of  the  columns  were  taken  to  depths  of  ten  or  twelve  feet,  the 
others  being  limited  in  depth  either  by  hardpan,  coarse  gravel  or  other 
obstruction  which  prevented  the  penetration  of  the  soil  auger;  some- 
times the  water  table  at  depths  of  less  than  ten  feet  produced  such 
mushy  conditions  in  the  soil  as  to  prevent  its  being  removed  by  the 
auger. 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  63 

Rich  Alluvial  Lands  and  Tule  Marshes.  The  rivers  of  the  San 
Joaquin  Valley  are  usually  bordered  by  narrow  bottom  lands,  the 
Merced  and  Kings  rivers  being  exceptions  where  they  enter  the  valley 
plains.  A  column  of  eight  feet  depth  was  taken  by  F.  E.  Johnson  from 
the  lands  of  Kings  River  near  Kings  River  post  office,  and  is  the  only 
representative  of  such  lands  from  this  valley.  The  surface  soils  of 
other  streams  have,  however,  been  examined  from  time  to  time  and 
their  humus  content  ascertained. 

The  tule  marshes  cover  a  very  large  region  at  the  junction  of  the  San 
Joaquin  and  Sacramento  rivers  and  are  divided  up  into  islands  by  many 
sloughs.  The  soil  of  these  islands  is  shallow  and  peaty  though  rich,  and 
water  appears  at  but  a  few  feet  below  the  surface.  There  are  localities, 
however,  where  a  deep  soil  may  be  found,  and  from  one  of  these  a 
column  of  twelve  feet  was  obtained  for  us  by  W.  W.  Mackie  of  the 
United  States  Bureau  of  Soils.  It  was  taken  from  a  few  miles  north- 
west of  Stockton,  and  is  an  excellent  representative  of  these  lands. 

Black  Adobe  Clay  Lands.  A  large  area  of  black  adobe  land  occupies 
an  area  in  San  Joaquin  County  extending  from  two  miles  north  of 
Calaveras  River  south  to  French  Camp  slough  and  from  the  tules  or 
marshes  of  San  Joaquin  River  eastward  toward  the  hills,  and  is  tim- 
bered with  oaks.  The  character  of  the  soil  is  shown  in  a  column  twelve 
feet  in  depth  taken  three  miles  southeast  of  Stockton. 

The  region  continues  southward  in  a  narrow  belt  along  the  base  of 
the  hills  into  Kern  County,  being  known  in  Tulare  County  as  "dry 
bog,"  because  of  its  tendency  to  break  up  into  small  fragments  when 
dry.  It  is  here  underlaid  by  a  reddish  clay  loam  from  which  it  is 
sometimes  separated  by  a  whitish  calcareous  or  siliceous  lime  and 
magnesian  bed  of  varying  thickness.  Two  columns  of  this  black  clay 
adobe  were  secured  from  near  Porterville,  one  of  which  appears  in  the 
table  of  analyses. 

On  the  west  side  of  the  valley  another  narrow  black  adobe  belt  reaches 
along  the  base  of  the  hills  from  west  of  Tracy  into  Merced  County  on 
the  south.  It  is  represented  by  a  column  of  ten  feet  taken  three  miles 
west  of  Tracy. 

Reddish  Clay  Lands.  A  prominent  and  wide  region  of  lands  of  this 
character  occupies  a  large  part  of  the  eastern  side  of  the  valley;  it  is 
narrow  on  the  north  in  San  Joaquin,  Stanislaus,  Merced,  and  Madera 
counties,  and  on  the  south  in  Tulare  and  Kern,  but  quite  wide  in  Fresno 
County.  It  is  the  southern  extension  of  the  belt  of  ' '  bedrock ' '  lands  of 
the  Sacramento  Valley.  It  is  largely  characterized  by  a  rocky  hardpan 
of  cemented  gravel  and  grit,  with  thicknesses  of  an  inch  to  as  much  as 
twelve  inches,  and  even  more,  and  occurring  at  depths  of  from  two  to 
six  or  eight  feet  below  the  surface ;  when  it  occurs  near  the  surface,  the 


64  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

hardpan,  because  of  its  irregular  bedding,  gives  rise  to  a  rolling  or  hog- 
wallow  feature.  An  excellent  soil  underlies  the  hardpan,  however,  and 
when  the  latter  is  broken  up  by  dynamite  good  results  in  tree  growth 
are  usually  obtained. 

Columns  of  this  land  were  obtained  from  a  few  miles  east  of  Fresno ; 
from  the  Kearney  Park;  from  Lindsay  in  Tulare  County;  and  from 
two  miles  southwest  of  Farmington,  San  Joaquin  County,  sent  by 
H.  Mueller. 

Delta  Plains  of  Kings  and  Kern  Rivers.  There  are  two  tracts  of  this 
class  of  lowlands  which  are  made  of  fine  sediment  brought  down  from 
the  Sierra  Nevada;  the  Coast  Range  on  the  west  contributing  little  or 
nothing  to  these  deltas,  as  its  streams  mainly  flow  westward  to  the 
Pacific. 

The  Mussel  Slough  region  bordering  Tulare  Lake  received  its  sedi- 
ment from  Kings,  Kaweah,  and  Tule  rivers  and  covers  a  very  large 
area.  It  is  timbered  with  oaks,  and  the  nature  of  its  soils  are  shown 
in  columns  twelve  feet  deep,  taken  respectively  from  near  Corcoran 
and  Armona. 

The  Kern  River  delta  further  south,  with  an  area  of  about  290  square 
miles,  is  also  timbered  with  oaks.  It  is  represented  in  the  soil  collec- 
tion by  a  column  taken  three  miles  southwest  of  Bakersfield.  Water 
was  reached  in  the  seventh  foot. 

Gray  Sandy  Loams  and  Sandy  Soils.  The  greater  part  of  the  San 
Joaquin  Valley  is  covered  with  gray  sandy  and  sandy  loam  soils  on  the 
east  side  of  the  valley  and  with  gray  clay  loams  on  the  west  side.  On 
the  east  side,  the  slope  of  the  valley  to  the  central  trough  is  wider 
than  on  the  west,  and  the  numerous  and  rapidly  flowing  streams  have 
brought  from  the  Sierra  much  sand  and  gravel,  which  comprises  from 
85  to  95  per  cent  of  the  composition  of  the  gray  soils.  Notwithstand- 
ing their  very  sandy  nature  these  lands  are  usually  deep  and  very 
highly  productive  under  adequate  rainfall  or  irrigation.  Calcareous 
hardpans  are  found  in  some  localities  in  irregular  sheets  and  at  various 
depths,  but  their  injurious  effects  can  be  obviated  in  orchards  by  blast- 
ing ;  a  good  soil  underlies  them.  Columns  of  these  lands  were  obtained 
from  Modesto,  Stanislaus  County ;  from  three  miles  west  of  Tulare ;  and 
from  a  few  miles  north  of  Exeter,  both  in  Tulare  County;  and  from 
near  Livingston,  Merced  County. 

Gray  Clay  Loam  Lands.  The  lands  on  the  west  side  of  the  valley 
are  quite  level  and  contain  more  clay  than  those  of  the  east  side.  There 
are  but  few  streams  on  the  west  side,  and  these  have  their  source  but  a 
short  distance  within  the  Coast  Range,  whose  drainage  is  almost  entirely 
westward.  These  west-side  lands,  therefore,  must  have  been  deposited 
from  the  waters  coming  from  the  Sierra  Nevada  after  they  had  dropped 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  65 

their  sands  and  gravels  on  the  east  and  become  more  quiet;  thus  per- 
mitting the  fine  silt  and  clay  to  settle.  The  soils  contain  from  15  to  24 
per  cent  of  clay.  Columns  were  obtained  from  south  of  Tracy,  San 
Joaquin  County ;  from  four  miles  west  of  Los  Bailos,  Merced  County ; 
and  from  Val  Verde,  two  miles  west  of  Mendota,  Fresno  County. 

Gray  Alkali  Lands.  Some  of  the  gray  loams  contain  large  amounts 
of  alkali  salts  in  small  areas  usually,  the  salts  consisting  of  varying 
proportions  of  carbonate,  sulfate  and  chlorid  of  sodium  and  frequently 
causing  serious  farming  difficulties.  Columns  of  soil  were  taken  from 
three  localities  which  contained  very  large  amounts  of  alkali.  These 
are  as  follows:  from  the  "white  ash"  lands  southwest  of  Fresno;  from 
the  old  experiment  station  tract  near  Tulare;  and  from  Miramonte, 
Kern  County. 

The  "white  ash"  soil,  so  called  because  of  its  fine  light,  ashy  and 
silty  nature,  was  taken  from  near  a  vineyard  in  Central  Colony,  sev- 
eral miles  southwest  of  Fresno,  and  is  the  representative  of  a  large 
region  lying  on  the  north  side  of  Kings  River  and  reaching  to  within 
two  miles  of  Fresno  and  eastward  toward  the  foothills  of  the  Sierra. 
The  soils  are  rich  and  have  been  largely  devoted  to  grape  growing. 
The  water  table  was  reached  at  a  depth  of  four  feet,  the  soil  assuming 
a  white  color,  and,  below  the  sixth  foot,  losing  all  traces  of  humus. 

The  Tulare  column  was  obtained  from  the  old  experiment  station 
tract  in  a  spot  where  all  vegetation  had  been  killed  by  the  alkali  salts. 

The  column  from  Miramonte,  fifteen  miles  west  of  Wasco,  represents 
what  seems  to  be  a  belt  of  low  lands,  or  what  was  once  a  slough  con- 
necting Tulare  Lake  with  those  southward  and  in  which  the  alkali  of 
the  lakes  had  accumulated  to  great  depths.  The  alkali  consists  chiefly 
of  the  sulfates  and  chlorids,  Glauber  and  common  salt,  and  in  this 
column  it  was  distributed  at  the  rate  of  one  half  of  one  per  cent  per 
foot,  or  a  total  approximating  233,000  pounds  for  the  twelve  feet.  No 
vegetation  other  than  scattering  alkali  weeds  was  seen. 

Talare  Lake  Bed.  A  large  part  of  the  bed  of  Tulare  Lake  was  a  few 
years  ago  quite  dry,  and  samples  of  the  soil  to  many  feet  depth  were 
sent  to  us  for  examination  as  to  their  alkali  content.  The  humus  per- 
centage of  each  foot  was  also  determined. 

The  table  below  gives  in  a  concise  form  the  relative  percentages  of 
humus  and  nitrogen  in  the  eight  soil  types  of  the  San  Joaquin  Valley, 
and  from  it  we  can  make  comparisons  more  easily  than  from  a  study  of 
the  soil  columns  themselves.  The  types  are  placed  in  the  order  of 
highest  to  lowest  composite  averages  of  humus  in  the  first  foot,  and 
this  almost  represents  the  succession  in  the  combined  upper  three  feet 
and  the  entire  column  respectively. 


66  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

Humus  and  Humus-nitrogen  in  Soils  of  the  San  Joaquin  Valley. 


Per  cent  humus 


First 
foot 


Upper  3  feet 


Average       Sum  of 
per  foot      per  cents 


Column,  12  feet 


Average       Sum  of 
per  foot     per  cents 


Per  cent  humus- 
nitrogen  in  soil 


First 
foot 


Upper 

3  feet 

average 


Tule  marshes 14.10 

River  alluvium 1.29 

Black  clays 1.09 

Red   lands   .95 

Delta  plains .81 

Gray  sandy  loams .66 

Gray   clay   loams .86 

Alkali  lands .34 

Tulare  Lake  bed .18 


16.68 

50.05 

.83 

2.50 

.82 

2.48 

.76 

2.28 

.49 

1.49 

.47 

1.40 

M 

2.04 

.30 

.90 

.14 

.42 

6.81 
.30 
.25 
.32 
.22 
.25 
.34 
.12 
.10 


81.75 

.83 

3.67 

.06 

3.02 

.06 

3.89 

.06 

2.59 

.04 

3.05 

.04 

4.12 

.06 

1.47 

.03 

1.20 

.01 

.04 
.04 
.05 
.03 
.03 
.04 
.02 
.01 


There  are  large  differences  in  the  amount  of  humus  in  the  several 
groups,  as  is  to  be  expected  from  soils  of  such  extremely  different 
characters,  the  highest  percentage  being  in  the  tule  marshes  and  the 
lowest  in  the  strong  alkali  lands  and  in  the  Tulare  Lake  bed. 

The  surface  soils  of  the  valley  are  not  rich  in  humus  as  a  rule,  and 
this  is  well  shown  in  these  tables.  Even  the  black  clays  and  loams, 
which  because  of  their  color  would  be  supposed  to  contain  high  per- 
centages, were  found  to  have  but  little  more  than  one  per  cent,  and  in 
some  instances  less  than  that.  Similarly,  the  alluvial  and  delta  soils  of 
Kings  and  Kern  counties  are  very  low  in  humus.  The  tule  marshes  in 
the  region  of  Stockton  are  naturally  rich,  because  of  the  great  amount 
of  vegetable  matter,  such  as  roots  and  leaves,  that  have  accumulated  in 
them,  and  we  find  as  much  as  14  per  cent  of  humus  in  the  first  foot 
and  19  in  the  second.  In  but  eight  of  the  individual  columns  (omitting 
the  Stockton  tule)  is  there  as  much  as  one  per  cent  in  the  surface  foot, 
the  highest  being  found  in  the  reddish  lands  of  Farmington,  and  the 
lowest,  .18  per  cent,  in  the  soil  of  Tulare  Lake  bed. 

In  the  upper  three  feet  the  amounts  of  humus  in  the  alluvium,  the 
black  clays  and  the  red  lands,  are  nearly  the  same ;  and  they  are  about 
equally  rich  in  nitrogen;  but  in  the  column  of  twelve  feet  depth  the 
black  clays  fall  behind  the  other  two,  and  the  gray  clay  loams  of  the 
western  side  of  the  valley  take  first  place  in  humus  content. 

The  river  alluvial  lands  then  are  richest  in  humus  in  the  first  foot  and 
upper  three  feet,  but  the  gray  clay  loams  contain  the  highest  percentage 
in  the  entire  column  of  twelve  feet.  The  individual  soil  richest  in  nitro- 
gen, except  the  marshes,  is  that  from  Farmington,  which  has  .14  per 
cent,  equivalent  to  more  than  5,000  pounds  per  acre  foot.  The  average 
through  all  of  the  soils  is  low. 

The  alkali  lands,  including  the  Tulare  Lake  bed,  contain  very  little 
humus  and  the  soils  are  very  poor  in  humus  nitrogen,  though  they  often 
have  quite  a  percentage  of  nitrates.     The  very  large  amount  of  alkali 


Bulletin  242] 


HUMUS   IN    CALIFORNIA   SOILS. 


67 


salts  they  contain  evidently  has  so  retarded  or  prevented  the  growth 
of  surface  plants  as  to  cut  off  the  supply  of  humus-forming  material. 

HUMUS  IN   THE  SOILS  OF  THE  FOOTHILLS  OF  THE  SIERRA   NEVADA. 

The  lower  foothills  of  the  Sierra  Nevada,  rising  from  the  Sacramento 
and  San  Joaquin  Valley  plains  to  an  elevation  of  2,500  feet  above  sea 
level,  form  an  important  fruit-bearing  region  of  the  State.  The  soils 
are  mainly  derived  from  the  slates  and  granites,  and  while  they  are 
deep  in  the  valleys  they  are  usually  shallow  on  the  hills,  though  the 
upturned  slates  permit  of  the  deep  penetration  of  plant  roots  between 
the  layers  to  moisture  and  food. 

Columns  of  these  soils  were  taken  from  the  valley  lands  near  Palermo, 
Butte  County ;  from  the  rolling  hills  of  the  old  experiment  station  tract 
east  of  Jackson,  Amador  County;  and  from  a  bluff  near  Newcastle, 
Placer  County,  which  afforded  a  deeper  sampling  than  did  the  other 
two  localities.  The  result  of  the  examination  of  the  soils  from  each  of 
the  localities  is  given  in  the  table  below,  in  a  depth  of  twelve  feet  for  the 
soil  from  Newcastle  and  of  eight  feet  each  for  the  others. 

Humus  and  Humus-nitrogen  in  Red  Soils  of  Foothills  of  Sierra  Nevada. 


Per  cent  humus 

Per  cent  humus - 
nitrogen  in  soil 

First 
foot 

Upper  3  feet 

Column 

.  12  feet 

First 
foot 

Average 
per  foot 

Sum  of 
per  cents 

Average 
per  foot 

Sum  of 
per  cents 

Upper 
3  feet 

Palermo    

Newcastle  

Jackson  

.96 
1.35 
1.07 

.51 

1.26 

.65 

1.52 
3.77 
1.96 

.29 
.47 
.33 

2.06 
5.64 
2.86 

.06 

.10 

.05 

.02 
.05 

.02 

The  red  clay  soils  of  Jackson  and  Palermo  are  quite  similar  in  the 
amount  of  humus  found  in  the  first  foot,  but  the  former  is  richer  below 
that  depth.  The  clay  is  quite  compact  and  close,  and  this  seems  to  have 
prevented  the  development  of  roots  to  the  depth  permitted  by  the  looser 
gravelly  granitic  soil  of  Newcastle,  in  which  there  is  more  humus.  The 
general  average  of  humus  in  the  first  foot  of  these  three  soils  is  1.12  per 
cent;  that  of  31  soils  of  the  foothills  previously  examined  is  1.05,  though 
it  is  found  to  be  higher  in  the  valleys  farther  up  in  the  mountains,  in 
the  regions  of  Auburn,  Grass  Valley,  Nevada  City,  and  Placerville. 

The  nitrogen  in  the  respective  soils  is  below  the  amount  it  should  be, 
except  in  the  upper  three  feet  of  the  Newcastle  column,  which  contains 
an  average  of  .10  per  cent,  or  approximately  4,000  pounds  per  acre  foot. 


68  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

SOIL  COLUMNS  OF  THE  COAST  RANGE  VALLEYS. 

The  Coast  Range  of  mountains  reaching  from  the  Oregon  state  line 
south  to  the  Mexican  border  has  but  few  agricultural  possibilities  out- 
side of  the  many  valleys  enclosed  between  the  mountain  ridges.  The 
country  north  of  Mendocino  County  is  especially  rugged,  and  the  valleys 
are  few,  but  southward  there  are  many  valleys  that  present  splendid 
agricultural  attractions,  and  we  have  endeavored  to  have  the  soils  of 
the  largest  and  most  important  ones  represented  in  the  columns  of  this 
series.  Of  course,  it  must  be  understood  that  in  each  valley  there  are 
a  number  of  soil-variations  and  graduations  from  the  hills  to  the  lower 
valley  center,  and  that  the  column  has  been  selected  to  represent  the 
best  and  most  extensive  of  these,  the  object  being  to  ascertain  to  what 
depth  and  in  what  percentage  the  humus  reaches  under  favorable  con- 
ditions. Fifteen  valleys  in  nine  counties  have  their  soils  represented  in 
the  series  of  columns,  and  in  the  accompanying  tables  are  arranged  in 
order  of  occurrence  from  north  to  south. 

"We  may  conveniently  follow  the  usual  subdivision  of  the  Coast  Range 
counties  and  arrange  the  table  into  the  counties  north  of  the  bay, 
embracing  seven  soil  columns;  the  bay  region  itself,  embracing  the 
country  east  and  west  of  the  bay  as  far  south  as  San  Jose,  represented 
by  eight  soil  columns ;  and  the  counties  south  of  the  bay  as  far  as  Santa 
Barbara,  represented  by  nine  soil  columns. 

North  of  the  Bay  Region. 

The  valleys  represented  in  this  section  of  the  Coast  Range  are  Russian 
River,  Santa  Rosa,  Los  Guillocos,  Sonoma,  Napa,  and  Yaca :  there  are 
other  important  though  much  smaller  ones  east  and  west  of  these  and  in 
the  counties  farther  north. 

Russian  River  Valley.  The  soil  columns  from  this  valley  were  taken 
from  the  alluvial  lands  of  the  hop  fields  belonging  to  T.  Boone  Miller 
six  miles  south  of  Healdsburg,  and  from  the  red  hills  three  miles  south- 
west of  Healdsburg,  Sonoma  County. 

Santa  Rosa  Valley.  The  western  part  of  the  valley  has  a  heavy  adobe 
soil,  which  is  not  as  largely  in  cultivation  as  is  the  more  loamy  land 
of  the  eastern  and  middle  part.  A  column  of  twelve  feet  depth  was 
taken  from  the  creek  alluvium  on  the  Vrooman  orchard  east  of  Santa 
Rosa. 

Los  Guillocos  Valley.  This  valley  is  not  very  wide  nor  long,  and  it 
opens  northward  into  Santa  Rosa  Valley.  Its  soil  is  a  reddish  loam  and 
is  represented  by  a  column  taken  a  short  distance  southeast  of  Kenwood, 
Sonoma  County. 

Sonoma  Valley.  The  valley  opens  southward  to  the  bay  and  is 
largely  covered  by  marsh  lands,  but  the  northern  part  is  higher  and 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  69 

comprises  better  lands.     A  black  adobe  clay  seems  to  be  the  prevailing 
soil,  and  a  column  of  this  was  taken  near  the  village  of  El  Verano. 

Napa  Valley.  The  soil  is  chiefly  loamy  in  nature,  interspersed  with 
some  adobe  belts  on  either  side.  A  column  of  the  former  was  obtained 
near  Yountville,  Napa  County,  to  a  depth  of  twelve  feet. 

Yaca  Valley.  This  valley  is  situated  among  the  foothills  on  the  west 
side  of  the  Sacramento  Valley,  into  which  it  opens,  and  is  noted  for  its 
early  fruits.  The  soil  is  chiefly  a  reddish  loam,  as  shown  in  the  column 
obtained  near  Vacaville. 

East  of  the   Bay    Region. 

Alameda  Plains.  The  bay  shore  rises  gently  eastward  to  the  foot  of 
the  Contra  Costa  hills,  a  distance  of  about  two  miles.  On  this  slope  the 
soil  is  largely  of  an  adobe  clay  nature.  The  city  of  Berkeley  is  situated 
on  this  slope,  the  University  of  California  being  at  the  foot  of  the  hills. 
A  column  of  the  clay  adobe  was  taken  from  the  Economic  Garden  on  the 
University  Campus.  Southward  from  Berkeley  and  Oakland  the  slope 
widens  into  a  plain  traversed  by  streams  from  the  Coast  Range  bordered 
by  wide  bands  of  a  more  loamy  soil,  and  upon  it  are  found  extensive 
farms  and  several  towns.  A  column  of  the  loam  was  taken  from  the 
land  of  Mrs.  Sanborn  south  of  Niles,  and  another  from  the  Meek  place 
near  Hayward. 

Eastward  across  the  Contra  Costa  hills  several  narrow  valleys  connect 
the  large  and  fertile  Livermore  Valley  with  the  bay  shore  on  the  north, 
and  representative  columns  of  soil  were  taken  from  three  of  these. 

Ignacio  Valley.  Along  Walnut  Creek  there  is  a  narrow  belt  of  black 
clay  loam  soil  bordered  by  land  more  adobe-like  in  nature  which  extends 
to  the  low  mesa  and  hills.  The  higher  land  on  the  mesa  and  bordering  it 
in  the  valley  has  a  stiff  and  black  adobe  clay  soil  about  three  feet  in 
depth  and  underlaid  by  a  whitish  material.  The  column  was  obtained 
from  the  place  of  Professor  F.  T.  Bioletti,  one  mile  north  of  Walnut 
Creek,  Contra  Costa  County. 

San  Ramon  Valley.  This  valley  is  a  continuation  southward  of 
Walnut  Creek  Valley,  but  wider  and  with  more  extensive  black  adobe 
soils,  a  column  of  which  was  obtained  in  the  vicinity  of  San  Ramon 
post  office,  Contra  Costa  County. 

Livermore  Valley.  The  soil  of  the  valley  plain  is  a  loam  while  that 
of  the  low  hills  of  the  west  and  south  is  reddish  and  gravelly.  A 
column  was  taken  to  a  depth  of  ten  feet  from  the  plain  in  the  Santa 
Rita  region,  Alameda  County. 


70  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

South  of  the  Bay  Region. 

Santa  Clara  Valley.  This  valley,  reaching  from  the  bay  of  San 
Francisco  southward  for  70  miles  into  San  Benito  County,  has  a  variety 
of  soils.  Around  the  bay  back  from  the  salt  marshes  is  a  black  clay 
adobe,  a  column  of  which  was  taken  from  the  Morse  Seed  Farm  near 
Santa  Clara.  The  soil  contained  4.43  per  cent  of  humus,  which  is  the 
highest  we  have  found  in  any  of  the  soils  of  the  State  except  the  marsh 
lands.  South  of  San  Jose  the  lands  are  more  loamy  in  character  and 
are  represented  by  a  column  taken  from  near  Gilroy,  by  F.  E.  Johnson. 
The  valley  west  of  San  Jose  has  a  soil  more  sandy  in  nature  and  more 
or  less  gravelly,  on  which  are  located  extensive  orchards.  A  column  of 
this  soil,  seemingly  representative  of  this  land,  was  taken  from  the 
El  Quito  ranch,  south  of  Saratoga. 

Pajaro  Valley.  The  soil  of  the  valley  proper  is  a  dark  loam,  while 
along  the  river  are  adobe  clays  and  clay  loams,  the  latter  being  devoted 
to  sugar  beet  culture.  The  valley  loam  is  alone  represented  in  the 
soil  column  series.  It  was  taken  from  the  apple-growing  section  on  the 
Watsonville  side  of  the  valley.  Another  column  of  soil  was  taken  from 
Watsonville  heights  one  mile  northwest  of  the  town.  At  eight  feet 
depth  a  mass  of  decomposed  granite  was  reached.  Both  columns  were 
taken  by  F.  E.  Johnson. 

Salinas  Valley.  The  lower  or  northern  part  of  the  valley  for  about 
50  miles  is  from  8  to  12  miles  wide,  but  to  southward  the  valley  is  very 
narrow.  Two  classes  of  soil  are  represented  in  the  series.  A  column  of 
15  feet  from  the  sandy  loam  lands  of  the  west  side  of  the  Salinas  River 
was  taken  at  Fort  Romie  near  Soledad ;  and  a  column  of  the  black  adobe 
lands  around  King  City,  Monterey  County,  was  kindly  sent  by  Mr.  R.  L. 
Adams,  formerly  of  the  Spreckels  Sugar  Beet  Company. 

Arroyo  Grande  Valley.  The  soil  of  this  narrow  but  important  valley 
is  of  a  dark  and  heavy  clay-loam  nature  to  the  depth  of  twelve  feet  and 
more.  Two  columns  were  obtained  by  F.  E.  Johnson,  one  near  the 
town  of  Arroyo  Grande,  the  other  from  the  farm  of  the  Routzahn  Seed 
Company  a  few  miles  to  the  westward,  the  only  apparent  difference 
being  a  darker  color  in  the  surface  foot  of  the  seed-farm  soil. 

Santa  Maria  Valley.  The  soil  is  chiefly  a  sandy  loam  of  a  brownish 
color  and  very  deep.  A  column  was  taken  by  F.  E.  Johnson  near  the 
sugar  beet  fields  west  of  the  town  of  Santa  Maria. 

Lompoc  Valley.  Three  chief  classes  of  soils  occupy  the  valley ;  adobe 
near  the  hills,  sandy  alluvium  near  Santa  Ynez  River,  and  an  inter- 
mediate type  of  clay  loam  between  them.  The  Burpee  seed-farm  is 
situated  on  the  clay  loam  lands,  and  a  column  of  soil  was  taken  there 
to  a  depth  of  12  feet,  when  water  was  reached. 


Bulletin  242] 


HUMUS   IN    CALIFORNIA   SOILS. 


71 


Humus  and  Humus-nitrogen  in  Valley  Lands  of  the  Coast  Range  Region. 
North  of  the  Bay  Region. 


Per  cent  humus 

Per  cent  humus- 
nitrogen  in  soil 

First 
foot 

Upper  3  feet 

Column.  12  feet 

First 
foot 

Upper 

Average 
per  foot 

Sum  of 
per  cents 

Average       Sum  of 
per  foot     per  cents 

average 
per  foot 

Russian  River  Valley 

Santa  Rosa  Valley 

1.76 

1.95 
2.25 
2.14 
2.61 
1.97 

1.55 
1.50 
1.74 
1.71 
1.98 
1.22 

4.64 
4.51 
5.21 
5.12 
5,94 
3.67 

1.01 
.92 
.92 
.84 
.95 
.71 

12.18 
11.10 

6.45 
10.05 
11.38 

8.53 

.08 

.09 
.13 
.11 
.11 
.13 

.06 
.08 

Los  Guillocos  Valley* 

Sonoma  Valley  _    _  _      

.10 
.05 

Napa  Valley  

Vaca  Valley _  _         ___ 

.08 
.08 

*7  feet  deep. 


East  of  Bay  Region. 

1.68 

1.39 

4.27 

.64 

9.79 

.09 

.64 

.67 

2.02 

.45 

4.46 

.06 

1.23 

1.19 

3.59 

.57 

6.90 

.07 

1.42 

1.34 

4.02 

.80 

9.68 

.08 

Alameda  Plains  ... 
Livermore  Valley  . 
San  Ramon  Valley. 
Ignacio  Valley 


.08 
.04 

.05 
.07 


South 

of  Bay  Region. 

3.97 

2.22 

6.65 

1.03 

11.05 

.10 

1.38 

1.18 

3.56 

.74 

6.64 

.09 

1.11 

.83 

2.50 

.55 

6.66 

.05 

3.14 

2.15 

6.47 

1.33 

16.60 

.16 

1.44 

1.13 

3.39 

.46 

5.57 

.11 

2.50 

1.86 

5.57 

1.09 

13.03 

.13 

Santa  Clara  Valley... 

Pajaro  Valley 

Salinas  Valley 

Arroyo  Grande  Valley. 
Santa  Maria  Valley... 
Lompoc  Valley 


.07 
.06 
.04 
.11 
.07 
.09 


The  soils  of  the  valleys  of  the  Coast  Range  are  remarkably  high  in 
their  humus  content  when  compared  with  the  other  soils  of  the  arid 
region.  The  general  average  of  the  State  is  1.25  per  cent  in  the  surface 
soil,  while  that  for  these  coast  valleys  is  1.94  per  cent.  But  especially 
does  this  difference  appear  when  we  note  the  many  individual  soils  in 
which  1  per  cent  of  humus,  is  found  at  depths  of  four,  five  and  even 
seven  feet.  In  nearly  all  of  the  columns  there  is  a  decrease  downward, 
indicating  that  the  humification  was  of  plant  roots  rather  than  of  vege- 
table matter  deposited  from  overflow  as  the  land  was  being  built  up. 

A  comparison  of  the  average  amounts  of  humus  in  the  soils  of  the 
three  divisions  shows  that  the  lands  of  the  valleys  north  and  south  of 
the  bay  region  are  richer  than  those  on  the  east,  both  in  the  surface 
foot,  the  upper  three  feet,  and  in  the  depth  of  twelve  feet.  Santa  Clara 
and  Arroyo  Grande  valleys  have  the  highest  percentages  in  the  first 
and  the  upper  three  feet,  while  Arroyo  Grande  and  Lompoc  valleys 
stand  first  as  regards  the  entire  depth  of  twelve  feet. 

It  is  interesting  to  note  that  Russian  River  Valley  on  the  north  and 
these  three  valleys  on  the  south  have  averages  of  more  than  one  per  cent 
for  the  entire  depth  of  twelve  feet,  the  only  instances  of  this  among  all 
of  the  soils  of  the  State  thus  far  examined  excepting  the  tule  marshes. 

It  is  also  to  be  noted  that  all  of  the  valleys  of  this  group  of  sixteen, 


72  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

except  Livermore  and  Salinas,  have  averages  of  more  than  one  per  cent 
of  humus  in  the  upper  three  feet,  and  that  Santa  Clara  and  Arroyo 
Grande  have  more  than  two  per  cent  each. 

The  percentage  of  nitrogen  in  the  first  foot  is  highest  in  the  valley  of 
Arroyo  Grande,  .16  per  cent  or  approximately  6,400  pounds  per  acre. 
Los  Guillocos,  Vaca  and  Lompoc  valleys  have  .13  per  cent  each,  Sonoma, 
Napa  and  Santa  Maria,  .11  per  cent  each,  and  Santa  Clara  has  .10  per 
cent,  while  all  others  have  less.  Among  the  individual  soils,  Gilroy  has 
.15  per  cent  and  Berkeley  .14  per  cent. 

In  the  upper  three  feet,  Arroyo  Grande  and  Guillocos  valleys  are  the 
richest  in  nitrogen,  the  approximate  amount  being  12,000  pounds  per 
acre  in  the  three  feet. 

SOIL   COLUMNS   OF  THE   SOUTHERN    CALIFORNIA    REGION. 

The  region  known  as  Southern  California  embraces  that  part  of  the 
State  lying  south  of  the  Sierra  Madre  Mountains,  and  includes  a  num- 
ber of  large  and  fertile  valleys  and  plains. 

Saticoy  Plain.  The  long  and  broad  slope  in  Ventura  County,  reach- 
ing from  the  mountains  southward  to  the  sea  shore  and  noted  for  its 
lima  bean  culture,  is  represented  by  two  soil  columns,  one  taken  by 
J.  B.  Neff  from  near  Mound  Schoolhouse  a  few  miles  east  of  Ventura,  and 
the  other  from  the  orange  grove  of  Mr.  N.  B.  Blanchard,  at  Santa  Paula. 

Santa  Clara  River  Delta.  This  comprises  a  broad  region  of  gray 
alluvial  land,  and  contains  more  or  less  alkali  salts  in  places.  "Water  is 
usually  found  at  a  depth  of  8  or  10  feet  below  the  surface.  The  delta 
is  noted  for  its  sugar-beet  culture.  A  column  was  taken  near  Spring- 
ville  by  J.  B.  Neff  to  a  depth  of  8  feet,  where  water  was  reached. 

Pleasant  Valley  Hill  Slope.  This  column  was  taken  from  the  sandy 
slope  of  the  hills  north  of  the  Southern  Pacific  Railroad  station  at 
Camarillo,  on  the  property  of  the  Citrus  Farms  Company. 

San  Fernando  Valley.  The  valley  of  San  Fernando  lies  north  of 
Los  Angeles  and  includes  about  200  square  miles.  Much  of  the  valley 
on  the  east  is  covered  by  debris  of  cobblestones,  gravel  sand  washed 
from  the  canyons  on  the  northeast,  but  the  rest  of  the  valley  has  sandy 
and  sandy  loam  soils,  with  some  heavier  clays  on  the  south. 

Two  columns  were  obtained  by  F.  E.  Johnson :  one  from  the  sandy 
lands  about  one  half  mile  north  of  Fernando,  representing  the  "gra- 
nitic wash  land"  at  the  foot  of  the  hills;  the  other  from  lowland  near 
the  old  Mission  two  miles  west  of  Fernando. 

San  Gabriel  Valley.  This  valley  lies  east  of  Los  Angeles  and  reaches 
from  the  mountains  southward  to  the  alluvial  plains.  It  is  watered  by 
the  San  Gabriel  River  and  bordered  on  the  east  by  the  Puente  Hills, 
and  San  Antonio  debris  cone.     Its  soil  is  a  sandy  loam.     A  column  of 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  73 

soil  was  taken  by  F.  E.  Johnson  from  the  neighborhood  of  Covina  and 
"represents  an  average  of  all  of  the  different  soil  types."  Another 
column  was  taken  by  Johnson  from  near  Monrovia,  and  represents  the 
heavier  type  of  soil,  the  greater  part  of  which  is  sandy  and  gravelly 
wash  from  the  hills. 

San  Bernardino  Valley.  The  eastern  portion  of  the  valley  of 
Southern  California,  known  as  the  San  Bernardino  Valley,  is  separated 
from  the  western  by  a  range  of  low  hills  and  by  the  debris  cone  of  the 
San  Antonio  Creek,  which  issues  from  its  valley  just  above  Pomona  and 
supplies  most  of  the  water  to  Chino  Creek,  which  empties  into  the  Santa 
Ana  River.  In  the  past,  from  time  to  time  portions  of  the  San  Antonio 
flow  has  been  diverted  into  the  San  Gabriel. 

The  valley  covers  a  large  area  and  comprises  a  large  variety  of  soil 
types,  a  few  of  which  are  represented  by  soil  columns.  The  valley  slopes 
toward  the  south  to  the  Rincon  Basin  and  Santa  Ana  River,  and  is 
bordered  by  a  rim  of  mesa  on  the  north,  east,  and  south. 

The  Valley  Plains.  The  soils  are  chiefly  of  a  sandy  nature,  of  excel- 
lent depth  and  good  fertility.  The  lowlands  are  sometimes  highly 
charged  with  alkali  that  has  been  brought  in  by  drainage  from  the 
higher  valley.  Several  types  of  soil  from  the  plains  are  represented  in 
the  columns. 

Sandy  loam  soils  of  the  central  part  of  the  valley  are  shown  in  a 
column  from  the  former  University  of  California  Experiment  Station 
tract,  three  miles  southwest  of  Ontario,  taken  by  J.  W.  Mills. 

Highly  sandy  soils,  apparently  accumulated  by  wind  storms  blowing 
in  from  the  mountain  passes  on  the  north,  lie  in  the  central  part  of 
the  valley  and  are  extensively  planted  in  grapevines,  the  roots  of  which 
penetrate  downward  for  very  many  feet.  A  column  of  this  type  of  soil 
was  secured  at  Guasti  from  the  land  of  the  Italian  Vineyard  Company. 

Alluvial  plains  of  the  Santa  Ana  River,  known  as  the  Victoria  Tract, 
a  few  miles  east  of  San  Bernardino. 

The  soils  of  the  valley  plain  are  all  quite  sandy  and  contain  but  small 
amounts  of  humus  and  of  nitrogen.  The  tendency  to  crust  over  and  to 
form  a  sandy  hardpan  or  plowsole  near  the  surface  is  quite  usual  with 
these  soils.  A  succession  of  good  green-manure  crops  grown,  turned 
under  deeply,  and  allowed  to  humify  properly  would  add  much  to  the 
value  and  fertility  of  these  lands. 

Low  Lands.  Near  the  border  of  Chino  Creek  there  are  low-lying 
lands  forming  a  wide  border  of  ' '  moist  lands ' '  which  do  not  need  irriga- 
tion. Ten  acres  of  these  near  Chino  formerly  formed  a  part  of  the 
Experiment  Station  of  Southern  California.     A  column  from  this  was 


?4  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

taken  by  F.  E.  Johnson.  Another  column  was  taken  near  Pomona 
from  a  marsh  spot  known  asa"  cienega. ' '  This  is  a  ' '  limited  area  show- 
ing growth  of  water-loving  plants,  appearing  sporadically  in  otherwise 
arid  surroundings — usually  hillsides  or  valley  margins — and  occa- 
sionally giving  rise  to  flowing  springs."  (Rept.  Cal.  Expt.  Sta.,  1892- 
1894,  page  185.) 

Mesa  Lands.  The  mesa  lands  that  border  the  valley  are  largely  of  a 
reddish  loam  type,  interspersed  on  the  north  side  by  deposits  of  sand 
and  gravel  from  the  hillsides. 

The  red  mesa  extends  eastward  up  the  Gorgonio  Pass  to  its  summit  at 
Banning,  where  it  forms  quite  a  high  plateau  above  Timoteo  canyon. 

A  column  of  the  sandy  mesa  of  the  north  side  was  taken  in  the  western 
part  of  Highlands  to  a  depth  of  twelve  feet,  in  which  the  sandy  soil 
continued  to  the  bottom. 

A  column  representing  the  red  clay  mesa  was  taken  near  Redlands  by 
F.  E.  Johnson.  The  upper  five  feet  were  of  reddish,  sandy  loam 
nature,  below  which  there  is  a  change  to  a  sandy  clay  and  finally  to  a 
gritty  stratum. 

A  column  from  Riverside  was  taken  from  Arlington  Heights  orchard 
lands  on  the  south,  and  we  were  able  to  reach  a  depth  of  eighteen  feet 
with  comparative  ease. 

Another  mesa  soil  column  was  taken  by  F.  E.  Johnson  from  nearly 
one  mile  south  of  the  town  of  Corona,  and  is  a  good  representative  of 
the  orchard  land  of  that  vicinity.  A  depth  of  twelve  feet  was  reached 
with  difficulty  because  of  the  presence  of  much  gravel. 

Los  Angeles  Alluvial  Plain.  The  three  rivers,  Los  Angeles,  San 
Gabriel  and  Santa  Ana,  have  each  brought  down  from  the  San  Bernar- 
dino Mountains  large  quantities  of  silt,  sand  and  clay,  and  formed  a 
large  body  or  region  of  alluvial  lands,  known  as  the  Los  Angeles  Alluvial 
Plains.  Each  river  preserves  its  own  course  through  these  plains,  and 
has  built  up  its  own  alluvial  plain  with  its  own  material  independently 
of  the  others.  We  thus  find  that  the  soils  of  the  San  Gabriel  are  of  a 
more  sandy  nature  than  those  of  the  Santa  Ana,  probably  because  of 
the  greater  velocity  of  the  river  current  over  a  shorter  distance.  The 
Santa  Ana  leaves  the  mountains  east  of  San  Bernardino  and  flows  by  a 
circuitous  route  along  the  southern  side  of  the  valley  and  thus  has  left 
most  of  its  coarse  material  behind  and  deposited  chiefly  clays  and  silts 
in  the  alluvial  plain. 

The  San  Gabriel  Plain  is  represented  by  three  columns.  One  was 
taken  from  the  place  of  Doctor  Twombly,  south  of  Fullerton,  to  a 
depth  of  ten  feet;  another  from  the  place  of  J.  B.  Neff,  near  Anaheim; 
while  the  third  column  was  taken  a  mile  south  of  Compton. 


Bulletin  242]  HUMUS  IN   CALIFORNIA   SOILS.  75 

The  Santa  Ana  Alluvial  Plain  is  represented  by  two  columns  taken 
by  F.  E.  Johnson.  One  of  these  from  two  miles  south  of  Santa  Ana,  to 
represent  a  considerable  area  of  heavy  black  adobe.  The  other  from 
Irvine,  six  miles  southeast  of  Santa  Ana,  represents  a  lighter  clay  loam 
soil.  Both  of  these  columns  are  from  the  south  side  of  Santa  Ana 
River. 

INTERIOR  VALLEYS. 

The  immediate  coast  line  is  bordered  by  a  wide  mesa  which  extends 
south  to  the  state  line,  interrupted  by  characteristic  deep  and  narrow 
valleys  or  occasional  streams.  The  valley  of  San  Diego  Eiver  is  wide 
and  affords  much  land  for  culture  purposes.  The  mesa  reaches  east- 
ward in  considerable  width  to  the  foot  of  the  higher  rolling  hills,  which 
rise  still  higher  into  the  San  Jacinto  Mountains.  Numerous  valleys 
small  and  large  lie  among  these  hills,  whose  soils  are  rich  and  pro- 
ductive. 

Fallbrook  Mesa.  The  hills  or  mesa  are  for  the  most  part  somewhat 
rolling  and  capable  of  cultivation  whenever  the  soil  is  of  sufficient  depth 
and  extent.  Fallbrook  affords  an  example  of  these  cultivable  hills,  and 
a  column  of  the  soil  was  taken  from  the  hillside  vineyard  of  Loma 
Ranch,  south  of  the  town.  The  red  clay  loam  soil  was  of  varying  thick- 
ness and  underlaid  by  a  mass  of  disintegrated  granite. 

Perris  Valley  lies  southeast  of  Riverside  at  the  western  foot  of  the 
San  Jacinto  Mountains.  It  is  about  10  miles  long  and  6  miles  wide,  and 
has  a  variety  of  soils  as  described  by  Professor  Hilgard  in  the  annual 
report  of  this  experiment  station  for  1894-95.  The  heavier  soil  from 
the  center  of  the  valley  about  a  mile  east  of  the  town  of  Perris  was 
selected  and  a  column  taken  by  F.  E.  Johnson. 

The  Valley  of  Escondido  is  large  and  productive,  lying  at  the  edge 
of  the  mountain.  Its  soil  is  a  loam.  A  column  was  taken  to  a  depth 
of  twelve  feet  by  F.  E.  Johnson  in  the  vineyard  of  C.  C.  Katzenburger 
on  the  north  side  of  the  valley. 

El  Cajon  Valley  lies  among  the  high  mountains  29  miles  east  of  San 
Diego  and  has  an  area  of  6  by  4  miles.  The  land  is  a  reddish  sandy 
loam  and  is  very  productive.  A  column  twelve  feet  in  depth  was  taken 
from  near  the  crossroads  by  F.  E.  Johnson. 


76 


UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 


Humus  and  Humus-nitrogen  in  Soils  of  Southern  California. 


Per  cent  humus- 

nitrogen  in  soil 

Upper  3  feet 

Column 

12  feet 

First 
foot 

First 

Average 

Sum  of 

Average 

Sum  of 

foot, 

3  feet, 

per  foot 

per  cents 

per  foot 

per  cents 

1.23 

.95 

2.86 

.52 

6.90 

.06 

.05 

.96 

.65 

1.96 

.34 

2.84 

.07 

.04 

.90 

.71 

2.12 

.43 

5.23 

.04 

.03 

.84 

.65 

1.96 

.30 

3.66 

.05 

.02 

.43 

.41 

1.22 

.16 

1.95 

.02 

.02 

.6/ 

.44 

1.33 

.28 

2.75 

.04 

.03 

4.2s 

2.59 

7.79 

1.20 

11.63 

.18 

.10 

1.16 

.84 

2.65 

.44 

5.26 

.07 

.05 

.35 

.59 

1.77 

.30 

3.60 

.05 

.03 

.55 

.37 

1.12 

.15 

1.78 

.03 

.02 

.47 

.29 

.89 

.13 

1.56 

.03 

.02 

.93 

.50 

1.50 

.18 

2.10 

.05 

.02 

Saticoy  Plain  

Santa  Clara  Delta 

Fernando  Valley 

Camarillo  hillside . 

San  Bernardino  plains 

San  Bernardino  mesa 

San  Bernardino  lowlands-. 

Alluvial  plains 

Perris  Valley 

Fallbrook 

Escondido  Valley 

El  Cajon  Valley 


The  nitrogen  percentages  are  nearly  all  too  low  and  indicate  the  great 
need  of  good  green-manuring  for  a  number  of  years  to  build  up  the 
upper  three  feet  of  soil  into  a  high  fertility.  This  is  needed  more  than 
phosphate  fertilization. 

There  are  but  six  of  the  twenty-five  soils  whose  surface  foot  contains 
more  than  one  per  cent  of  humus;  there  are  but  five  others  that  have 
more  than  .75  per  cent,  and  there  are  five  whose  humus  falls  even  below 
.50  per  cent. 

The  lands  represented  by  these  columns  from  Southern  California  are 
under  such  continuous  cultivation  that  the  surface  foot  is  hardly  a 
proper  unit  of  comparison ;  a  depth  of  three  feet  would  be  more  nearly 
correct,  for  in  that  is  usually  found  the  mass  of  feeding  roots,  and  no 
disturbing  irregular  conditions  exist.  The  general  average  of  the 
total  amount  in  the  three  upper  feet  (sum  of  per  cents)  of  the  columns 
(omitting  that  of  the  Pomona  Arroyo),  is  1.98,  or  an  average  of  .66 
per  cent  per  foot. 

The  Santa  Ana  adobe  and  Chino  moist  land  have  each  above  4.50 
per  cent  in  the  upper  3  feet  and  Mound  has  3.11  per  cent,  but  all  others 
fall  below  the  latter.  Six  of  the  columns  have  more  than  two  per  cent 
each,  while  on  the  other  hand  three  have  each  a  sum  of  less  than  one 
per  cent  in  the  three  feet  or  an  average  of  but  .25  per  cent  per  foot. 

The  humus  in  these  soils  is  with  a  few  exceptions  not  especially  rich 
in  nitrogen,  and,  as  a  consequence,  the  soil  is  but  meagerly  supplied 
with  that  element. 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  77 

SOIL  COLUMNS  OF  THE  NORTHEASTERN   LAVA-BED  REGION. 

The  lava-bed  region,  comprising  a  large  portion  of  the  northeastern 
part  of  the  State,  reaches  north  from  the  Sierra  Nevada  Mountains  into 
Oregon,  and  is  a  region  of  lava-bed  plateaus  and  hills  interspersed  with 
occasional  valleys  that  are  capable  of  cultivation  to  a  large  extent  in 
grain  and  alfalfa. 

Honey  Lake  Valley.  This  valley  with  its  large  lake  lies  between  the 
foot  of  the  Sierra  and  the  lava  hills  on  the  north,  and  has  an  elevation 
of  about  4,000  feet  above  sea  level.  It  is  divided  into  the  Honey  Lake 
Valley  proper  and  the  East  Side  Valley,  which  extends  from  the  Lake 
eastward  into  the  desert  region. 

Honey  Lake  occupies  the  lower  part  of  the  valley  and  is  bordered 
on  all  sides  by  lands  which  are  being  brought  under  cultivation  in  grain 
and  alfalfa,  except  on  the  east,  which  is  of  a  more  sandy  and  alkali 
nature.  A  column  of  soil  was  taken  to  a  depth  of  ten  feet  from  near 
Standi sh  on  the  north  side  of  the  valley,  humus  being  found  only  in 
the  upper  five  feet ;  a  large  and  luxuriant  growth  of  alfalfa  covered  the 
adjoining  fields. 

Another  column  of  soil  taken  by  Professor  G.  W.  Shaw  from  a  strong 
alkali  tract  bordering  the  lake  on  the  east  side  near  Amedee,  contained 
but  little  humus. 

East  Honey  Lake  Valley.  This  desert-like  region  comprises  that 
portion  of  Honey  Lake  Valley  in  Lassen  County  that  reaches  eastward 
from  the  lake  into  Nevada  at  an  elevation  of  about  100  feet  more  than 
the  lands  around  the  lake,  and  lies  between  hills  of  lava  debris.  The 
width  is  about  15  miles,  but  increases  to  much  more  toward  the  state 
line.  The  soil  of  the  plain  is  for  the  most  part  quite  free  from  alkali 
salts,  which  only  appear  here  and  there  on  the  surface ;  but  toward  the 
state  line  at  lower  levels  the  alkali  is  more  abundant.  On  the  north  side 
of  this  plain  the  soil  is  quite  level  and  sandy,  with  a  reddish  sandy 
subsoil. 

A  wide  belt  of  alluvial  land  borders  Skedaddle  Creek  with  a  depth  of 
three  or  four  feet  near  the  creek.  Beneath  this  there  is,  as  shown  in  a 
well  on  the  place  of  A.  L.  Spoon  at  Stacy  Station,  two  feet  of  sand, 
twenty  feet  of  a  calcareous  clay,  underlaid  in  turn  by  blue  sand  and 
clay.  A  column  of  soil  was  taken  for  examination  from  this  place  to  a 
depth  of  twelve  feet.  Its  upper  foot  contained  .64  per  cent  of  humus, 
the  second  foot  1.26  per  cent  and  below  this  the  humus  percentage 
decreased  to  .20  per  cent  in  the  twelfth  foot. 

It  is  interesting  to  note  here  that  a  well  on  the  place  of  Mr.  Caudle, 
north  of  Stacy,  exposed  three  feet  of  a  reddish  soil,  three  feet  of  sand, 
seven  feet  of  boulders  and  fifteen  feet  of  white  calcareous  clay;  below 

3— bul242 


78  UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION. 

this  appeared  blue  clay  to   a   depth  of  320   feet  from  the  surface, 
water  being  reached  at  that  depth. 

In  the  center  of  the  valley  the  surface  of  the  land  is  in  low  ridges,  the 
sandy  soil  being  blown  into  hillocks;  the  soil  is  underlaid  by  a  very 
compact  gray  silty  soil  to  ten  feet;  then  beneath  that  is  ten  feet  of  a 
fine  sand,  followed  by  ten  feet  of  a  coarse  sand  in  which  water  is  struck 
in  wells.  Beneath  this  lies  a  blue  clay  of  fifty  feet  or  more  thickness. 
A  column  of  soil  was  taken  in  this  land  to  twelve  feet  depth  from  near 
the  place  of  Dr.  B.  B.  Bolton  four  miles  north  of  Calneva.  In  this  the 
humus  occurred  in  each  foot  of  the  column,  but  in  very  small  amounts. 
On  the  south  of  the  Western  Pacific  Railroad  at  Calneva  to  the  moun- 
tains the  soil  is  coarsely  sandy. 

Madeline  Plains.  Passing  north  from  Honey  Lake  Valley  across 
hills  covered  with  beds  of  lava  we  come  to  the  Madeline  Plains,  which 
occupy  a  large  and  almost  level  basin  (probably  once  an  inland  lake) 
at  an  elevation  of  5,200  feet  above  sea  level.  Its  area  is  approxi- 
mately 150  square  miles.,  very  irregular  in  outline,  and  bordered  on  all 
sides  by  lava  hills.  Its  soil  is  a  dark  and  very  compact  clay  underlaid 
at  three  or  more  feet  by  a  light  colored  marl  of  a  hardpan  nature  and 
upwards  of  75  feet  in  thickness,  as  shown  in  well  borings.  A  column  of 
this  soil  four  feet  in  depth  was  obtained  from  the  plain  to  westward  of 
the  place  of  W.  C.  Brockman.  Previous  analyses  of  other  samples  show 
fair  amounts  of  phosphoric  acid.  Grass  and  grain  are  said  to  do  well 
on  this  plain.  The  surface  foot  was  found  to  contain  .52  per  cent  of 
humus,  and  the  second  foot  .60  per  cent,  but  below  this  the  clay  was 
almost  free  from  it.  The  soil  contains  about  .04  per  cent  of  humus 
nitrogen. 

Pit  River  Valley.  Pit  River,  with  its  source  at  the  foot  of  the 
Warner  range  of  mountains,  passes  through  a  number  of  valleys  as  it 
flows  westward  into  the  Sacramento  River.  The  town  of  Alturas  is 
located  in  one  of  these  valleys  at  the  junction  of  the  two  forks  of  the 
river.  The  soil  of  the  valley  is  chiefly  meadowland,  with  water  at  a  few 
feet  and  partly  grown  in  tules,  but  affording  large  alfalfa  tracts.  A 
column  of  six  feet  was  taken  from  an  alfalfa  field  near  the  town.  The 
valley  is  bordered  by  lava-bed  mesas  and  hills.  Goose  Lake  Valley  to 
northward  and  reaching  into  Oregon  has  a  similar  meadowland  soil 
reaching  from  the  lake  eastward  to  the  foot  of  the  mountains,  where  the 
disintegrated  debris  afford  some  higher  land  on  which  orchards  are 
planted. 

Klamath  Lake  Marshes.  A  column  from  the  tule  marshes  of  Klamath 
Lake,  Butte  Valley,  Siskiyou  County,  was  obtained  for  us  by  Mr.  L.  S. 
Robinson  for  examination. 


Bulletin  242] 


HUMUS   IN    CALIFORNIA    SOILS. 


?9 


Surprise  Valley.  Eastward  from  Alturas,  the  Warner  range  of 
mountains  separates  the  Pit  River  Valley  from  Surprise  Valley  with 
its  three  large  lakes.  The  land  of  this  valley  on  the  east  is  strongly 
charged  with  alkali  salts,  but  on  the  west  the  broad  slope  from  the 
mountains  to  the  lake  presents  excellent  agricultural  possibilities,  the 
production  of  alfalfa  seed  being  quite  a  prominent  industry.  A  column 
of  soil  ten  feet  deep  (to  water)  was  obtained  from  the  valley  two  miles 
south  of  Cedarville,  and  another  column  of  four  feet  from  the  meadow- 
land  that  forms  a  broad  border  to  the  lake  and  in  which  water  was 
struck  at  four  feet. 


Humus  and  Humus-nitrogen  in  Soils  o^ 

the  Lava-bed 

Region. 

Per  cent  humus 

Per  cent  humus- 
nitrogen  in  soil 

First 
foot 

Upper  3  feet 

Column.  12  feet 

First 
foot 

Average 
per  foot 

Sum  of 
per  cents 

Average 
per  foot 

Sum  of 
per  cents 

3  feet 

Honey  Lake  Valley      _  __  _ 

.54 
3.05 
4.29 
2.71 
3.75 

.45 
1.84 
2.25 
1.89 
3.32 

1.35 
5.51 
6.75 
5.67 
9.97 

.23 
1.20' 
1.10 

2.73 

7.23 

10.98 

.03 
.06 
.05 
.09 
.34 

.02 

Pit  River  Valley 

Surprise  Valley  __  _      _  _  _ 

.06 

.04 

Surprise  Valley  meadows 

.09 

Klamath  marsh _. 

1.81 

14.52 

.29 

The  soils  from  the  Honey  Lake  Valley  contain  very  little  humus  even 
in  the  surface  foot,  but  it  is  found  throughout  the  entire  column  except 
at  Standish,  and  it  is  very  poor  in  nitrogen.  The  humus  is  apparently 
derived  from  the  debris  and  roots  of  the  sagebrush  and  alkali  weeds 
that  grow  on  the  plain. 

With  an  abundant  water  supply  and  the  turning  under  and  humifica- 
tion  of  some  good  legume  crop  there  is  no  reason  why  the  lands  of  East 
Honey  Lake  Valley,  at  their  elevation  of  4,000  feet  above  sea  level, 
should  not  produce  crops  suitable  to  that  altitude  as  well  as  the  lands 
of  Imperial  Valley  which  are  below  sea  level,  though  climatic  conditions 
naturally  would  control  the  kind  of  crops  grown. 

The  column  taken  from  Standish  on  the  north  side  of  the  lake  and 
from  an  alfalfa  field  is  surprisingly  low  in  humus  below  the  surface 
foot.  The  underlying  whitish  limy  loam  seems  to  have  restricted  the 
development  of  plant  roots  to  the  upper  four  feet.  The  humus  is  also 
poor  in  nitrogen  and  was  probably  derived  from  the  meager  roots  of 
sage  and  alkali  weeds.  A  soil  previously  taken  from  the  Susanville 
Meadows  had  only  .33  per  cent  of  humus,  and  another  from  two  miles 
west  of  Amedee  had  but  .29  per  cent.  The  Pit  River  Valley  clay  soil 
is  under  cultivation  in  alfalfa,  and  the  amount  of  humus  is  large, 
though  very  poor  in  nitrogen.  On  the  other  hand,  the  Klamath  column 
is  from  tule  marsh  lands,  containing  a  larger  proportion  of  decaying 
vegetable  matter,  and  consequently  is  quite  rich  in  humus  in  each  of  the 


80  UNIVERSITY   OP   CALIFORNIA — EXPERIMENT   STATION. 

upper  four  feet.  The  humus-  is  especially  rich  in  nitrogen,  and,  as  a 
consequence,  the  soil  is  also  enormously  rich  in  it  through  its  upper 
four  feet.  The  fifth  and  sixth  feet  are  largely  made  up  of  diatomaceous 
earth  in  which  the  humus  has  suddenly  diminished  to  less  than  one  per 
cent,  while  beneath  this  there  is  but  a  trace  of  humus. 

The  surface  soil  of  the  Cedarville  loam  is  surpassed  in  its  percentage 
of  humus  (4.29  per  cent)  by  only  the  black  clay  of  Santa  Clara  and  the 
marsh  lands  among  all  of  the  soils  of  the  State  thus  far  examined,  and 
it  ranks  as  fifth  with  regard  to  the  amount  in  the  three  upper  feet.  The 
percentage  throughout  the  entire  column  of  ten  feet  is  quite  high.  This 
high  humus  content  may  be  due  to  the  alfalfa  crops  that  have  been 
produced  for  seed  on  this  soil  for  a  number  of  years  past,  as  a  soil  from 
another  locality  near  Cedarville  examined  ten  years  ago  contained  but 
1.56  per  cent  in  the  surface  foot.  The  humus  is,  however,  remarkably 
weak  in  nitrogen  (1.14  per  cent)  if  such  was  its  origin. 

The  meadow  soil  lying  at  a  lower  level  is  very  similar  to  that  of 
Alturas  in  its  humus  content. 

SOIL  COLUMNS  OF  THE  "DESERT"  PLAINS. 

The  term  ' '  desert ' '  is  here  applied  to  the  extent  of  country  with  scant 
rainfall  and  having  a  vegetation  of  sagebrush  and  largely  devoid  of 
grasses ;  a  country  whose  soils  are  usually  rich  in  the  mineral  elements 
of  plant  food  and  which  are  remarkable  for  their  fertility  when  properly 
cultivated  and  abundant  irrigation  water  is  used.  The  reason  for  this 
fertility  lies  partly  in  the  fact  that  the  humus,  though  small  in  amount, 
is  with  its  nitrogen  well  distributed  throughout  a  depth  of  twelve  feet 
and  more,  in  a  soil  whose  sandy  or  silty  texture  permits  deep  rooting 
of  plants. 

Some  of  the  valleys  have  with  irrigation  been  brought  under  cultiva- 
tion and  settlement,  and  from  these  a  few  soil  columns  were  secured. 

Imperial  Valley.  This  newly  settled  part  of  the  State,  the  bed  of  Sal- 
ton  basin,  which  on  drying  up  became  a  desert  until  reclaimed  by  irriga- 
tion, largely  lies  below  the  level  of  the  sea.  Its  soils,  derived  from  the 
sediment  of  the  Colorado  River,  have  a  peculiar  light  pinkish  tint,  and 
are  made  up  of  alternating  strata  of  silt  and  a  very  plastic  impervious 
clay  of  varying  thickness.  When  this  clay  forms  the  surface  soil,  the 
difficulties  of  cultivation  and  irrigation  are  very  great,  but  when  the 
clay  lies  at  a  depth  of  several  feet  below  the  surface  of  silty  soil,  the 
reverse  is  true.  This  peculiar  type  of  land  is  represented  in  the  series 
by  two  columns  of  soil,  one  from  the  vicinity  of  Imperial  and  the  other 
from  near  El  Centro;  these  and  that  from  Coachella  were  taken  by 
F.  E.  Johnson. 

Coachella   Valley.     A  column   was   obtained   from   the   vicinity   of 


Bulletin  242] 


HUMUS  IN   CALIFORNIA   SOILS. 


81 


Coachella  and  represents  the  higher  and  more  sandy  lands  that  bordered 
the  old  Salton  Lake  of  the  Imperial  country. 

Mojave  River  Mesa.  This  mesa  or  plain  is  formed  by  accumulation 
of  granitic  debris  from  the  Sierra  Madre  Mountains  on  the  south  and 
reaches  far  out  toward  Barstow,  San  Bernardino  County.  This  debris 
is  coarse  and  quite  compact,  and  in  the  neighborhood  of  Victorville  is 
said  to  have  a  thickness  of  35  feet  or  more.  It  is  here  overlaid  by  about 
three  feet  of  a  gray  sandy  soil,  also  quite  compact  and  supporting  a 
sparse  vegetation  of  weeds.  A  column  of  eleven  feet  was  obtained  three 
miles  west  of  Victorville.  The  soil  was  found  to  contain  but  .13  per 
cent  of  humus  in  the  surface  foot,  .14  per  cent  in  the  second,  .10  per 
cent  in  the  third,  and  .08  per  cent  in  the  coarse  sand  of  the  fourth  foot. 
There  were  but  traces  of  nitrogen  in  the  humus. 

Owens  River  Valley.  The  agricultural  lands  of  this  valley  lie  chiefly 
on  the  western  side  of  Owens  River  and  are  formed  from  the  debris  of 
the  adjoining  Sierra  Nevada.  A  column  of  soil  was  secured  through  the 
kindness  of  Mr.  W.  K.  "Winterhalter  of  San  Francisco. 


Humus  and  Humus- 

NITROGEN   IN    SOILS   OF 

the  "Desert" 

Plains. 

Per  cent  humus 

Per  cent  humus- 
nitrogen  in  soil 

First 
foot 

Upper  3  feet 

Column,  12  feet 

First 
foot 

Upper 
3  feet, 
average 

Average 
per  foot 

Sum  of 
per  cents 

Average 
per  foot 

Sum  of 
per  cents 

Imperial  Valley 

.28 
.32 
.13 
.31 

.24 
.23 
.12 
.24 

.72 

.68 
.37 
.73 

.22 
.15 
.04 
.13 

2.68 

1.86 

.45 

1.56 

.02 

.01 

trace 

.01 

.01 

Coachella  Vallev     - 

.01 

Mojave  River  Plains 

Owens  Valley 

trace 

.01 

It  was  to  be  anticipated  that  the  soils  of  what  are  known  as  the 
desert  plains  of  the  eastern  and  southeastern  part  of  the  State  would  be 
very  poor  in  humus  because  of  their  very  sandy  nature  together  with 
small  rainfall,  extreme  summer  heat  and  scant  vegetation,  but  it  was  a 
surprise  to  find  that  humus  occurred  at  depths  of  twelve  or  more  feet 
below  the  surface.  The  soil  poorest  in  humus  is  that  from  the  mesa 
plain  just  west  of  Victorville,  in  which  plant  roots  were  found  to  a 
depth  of  three  feet  only,  the  underlying  material  being  too  compact  for 
root  penetration.  It,  however,  supported  a  growth  of  yucca  and  desert 
weeds,  and  on  the  same  mesa  with  presumably  the  same  soil  though 
deeper,  near  Hesperia  there  are  a  few  orchards.  A  glance  at  the  table 
shows  that  there  is  nearly  the  same  percentage  of  humus  in  the  first 
foot  of  each  of  the  columns  and  very  little  difference  in  the  total  amount 
in  the  upper  three  feet  of  the  columns. 

The  very  unequal  distribution  in  the  El  Centro  column  is  somewhat 
surprising,  for  it  might  readily  be  supposed  that  the  small  amount  in 


82 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


the  surface  foot  would  indicate  that  there  was  scarcely  any  in  the  lower 
depths;  whereas  we  find  higher  percentages  in  the  fourth,  fifth,  eighth, 
and  tenth  foot  respectively  than  in  either  of  the  upper  three  feet.  It 
is  interesting  to  note  that  there  is  more  in  the  lower  half  of  the  column 
than  in  the  upper.  The  humus  of  these  columns  is  not  quite  as  rich  in 
nitrogen  as  that  of  the  soils  from  other  parts  of  the  State,  and  that  of 
the  Bishop  column  is  extremely  low.  The  nitrogen  of  the  soil  is  not 
more  than  .01  per  cent  or  about  400  pounds  per  acre  foot. 

Individual    Soil    Columns    Having   the    Highest    Humus   Content. 

In  looking  over  the  109  columns  of  soil  taken  from  the  various  agri- 
cultural regions  of  the  State  we  find  that  eighteen  have  each  more  than 
two  per  cent  of  humus  in  the  surface  foot,  and  thirty-two  others  have 
more  than  one  per  cent,  the  remaining  fifty-nine  having  less  than  that. 
We  also  find  that  nine  of  the  columns  have  each  an  everage  of  more 
than  two  per  cent  of  humus  in  each  of  the  upper  three  feet,  and  twenty- 
five  others  have  an  average  of  more  than  one  per  cent,  all  others  falling 
below  the  one  per  cent.  In  the  distribution  of  the  humus  through  the 
entire  twelve  feet  of  the  columns  there  are  ten  which  give  an  average 
of  more  than  one  per  cent  for  each  foot,  and  twenty-five  others  whose 
average  is  above  one  half  of  one  per  cent. 

In  the  following  table  we  have  placed  the  names  of  the  twenty 
localities  which  have  as  much  as  1.95  per  cent  in  the  surface  foot,  and 
the  twenty  which  rank  highest  in  averages  of  the  upper  three  feet  and 
in  the  entire  column  of  ten  or  twelve  feet. 

Soil  Columns  Having  the  Highest  Humus  Percentages. 


In  first  foot 


Average  of  upper  3  feet 


Average  of  entire  column  of 
10  or  12  feet 


Stockton  tule 14.10 

Pomona  cienega 6.23 

Santa  Clara  adobe.  4.43 

Cedarville   4.29 

Arroyo  Grande  Seed 

Farm  3.78 

Klamath  marsh 3.75 

Alturas    3.05 

Gilroy 2.76 

Cedarville  meadows  2.71 

Yountville 2.64 

Lompoc  Seed  Farm.  2.50 

Arroyo  Grande 2.50 

Santa  Ana  adobe___  2.42 

Chino  moist  land___  2.31 

Kenwood  2.25 

El  Verano  adobe___  2.14 

Berkeley  adobe 2.13 

Farmington   2.04 

Vacaville   1.97 

Santa  Rosa 1.95 


Stockton  tule 16.68 

Pomona  cienega 3.67 

Santa  Clara  adobe_  3.63 

Klamath  marsh 3.32 

Cedarville  2.25 

Gilroy    *_ 2.23 

Arroyo  Grande 2.16 

Arroyo  Grande  Seed 

Farm  2.01 

Berkeley  adobe 2.01 

Yountville  1.98 

Cedarville  Meadows  1.89 

Lompoc  Seed  Farm.  1.86 

Alturas    1.84 

Keriwood  1.74 

El  Verano  adobe 1.71 

Farmington    1.65 

Santa  Ana  adobe___  1.63 

Russian  River 1.55 

Chino    1.52 

Glenn 1.51 


Stockton  tule 6.81 

Arroyo  Grande 1.39 

Santa  Clara  (10  feet)  1.33 

Pomona  cienega 1.28 

Arroyo  Grande  Seed 

Farm  1.27 

Gilroy 1.14 

Cedarville  (10  feet).  1.10 

Lompoc  Seed  Farm.  1.09 

Berkeley   1.04 

Russian  River 1.01 

Yountville    .95 

Santa  Rosa .92 

El  Verano  (10  feet)_  .84 

Walnut  Creek .80 

Hayward .77 

Davis  University 

Farm  .75 

Watsonville   .74 

Chico .73 

Vacaville   .71 

Glenn .69 


Bulletin  242] 


HUMUS   IN    CALIFORNIA    SOILS. 


83 


Composite  Columns  of  Agricultural   Regions. 

In  the  following  table  are  given  the  averages  of  each  of  the  agri- 
cultural regions,  embracing  all  of  the  109  columns  representing  the 
State  at  large,  taken  from  thirty-seven  counties.  The  tule  marshes  of 
Stockton,  Pomona,  and  Klamath  are  placed  in  a  column  by  themselves. 
In  some  of  the  individual  columns  that  form  the  composite  for  each 
region  either  a  depth  of  twelve  feet  was  not  secured  or  the  humus  itself 
was  not  found  to  that  depth. 

Composite  Averages  of  Agricultural  Regions  (Per  Cents). 


Sacra- 
mento 
Valley 


18 
columns 


San 
Joaquin 
Valley 


23 

columns 


Coast 
Range 
valleys 


24 
columns 


Southern 
Cali- 
fornia 


25 
columns 


Sierra 
Nevada 
foothills 


columns 


N.  E. 
lava -be els 
valleys 


columns 


"Desert" 
plains 


5 
columns 


Tule 
marshes 


columns 


1  foot 

2  feet 

3  feet 

4  feet 

5  feet 

6  feet 

7  feet 

8  feet 

9  feet 

10  feet 

11  feet 

12  feet 


1.04 
.75 
.58 
.45 
.36 
.32 
.23 
19 
.18 
.17 
.16 
.15 


.80 

1.94 

.51 

1.47 

.37 

1.13 

.25 

.93 

.23 

.77 

.17 

.67 

.14 

.59 

10 

.49 

18 

.41 

06 

.39 

06 

.27 

04 

.32 

1.12 
.71 
.57 
.39 
.18 
.14 
.18 
.10 


1.55 
.92 
.48 
.40 
.21 
.18 
.13 
.12 
.11 
.09 
.03 
.03 


.26 
.19 
.17 
.25 
.18 
.13 
.13 
.14 
.12 
.13 
.15 
.13 


8.04 

8.59 

7.05 

5,52 

2.65 

1.45 

.78 

1.64 

.68 

.30 

.21 

.29 


In  12  Feet. 


Sum  of  per  cents.-. 
Nitrogen  in  humus. 
Nitrogen  in  soil 

4.58 

5.45 

.03 

2.91 

6,53 

.02 

9.38 
5,15 

.04 

3.93 
5.54 

.02 

3.93 

5.64 
.03 

4.25 

3,69 

.03 

1.96 

4.69 

.01 

37.20 

5.63 

.20 

In  Upper  3  Feet;  Range  of  Most  Annual  Plant  Roots. 


Sum  of  per  cents— 
Nitrogen  in  humus. 
Nitrogen  in  soil 

2.37 

5.79 

.04 

1.68 
6.27 

.04 

4.54 
5.13 

.07 

1.98 

5.74 

.03 

2.40 

5.40 

.05 

2.95 

3.79 

.05 

.62 

4.97 
.01 

24.68 
5.75 

.44 

In  Surface  Foot. 


Nitrogen  in  humus. 
Nitrogen  in  soil 


5.68 

6.08 

5.43 

6.50 

5.93 

3.53 

5,03 

.05 

.05 

.10 

.05 

.07 

.05 

.02 

5.35 
.47 


On  glancing  at  the  table,  attention  is  first  called  to  the  depth  of 
twelve  feet  to  which  humus  reaches  in  all  of  the  columns  except  that 
of  the  Sierra  Nevada  foothills,  the  lava-bed  meadows  and  the  tule 
marshes  where,  because  of  the  underlying  country  rock  on  the  one  hand 
and  of  water  on  the  other,  the  depths  are  limited  to  eight,  ten  and  seven 
feet  respectively.  In  some  of  the  columns  the  amount  of  humus  is  so 
high  in  the  twelfth  foot,  especially  in  that  of  the  valleys  of  the  Coast 
Range,  as  to  leave  no  doubt  of  its  being  found  at  a  greater  depth  had 
the  examination  been  made.     In  fact,  the  column  of  Fort  Romie  was 


84  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

carried  through  fifteen  feet,  and  .41  per  cent  of  humus  with  6.83  per 
cent  of  nitrogen  was  found  in  the  lowest  foot. 

The  next  point  of  interest  is  the  small  amount  of  humus  in  the  first 
foot  of  each  of  the  columns  excepting  those  of  the  meadow  lands  and 
the  tule  marshes.  This  is  especially  noticeable  in  the  composite  of  the 
San  Joaquin  Valley  and  in  that  of  the  "Desert"  plains.  The  general 
average  for  all  of  the  columns  excluding  the  marshes  is  1.16  per  cent. 

Another  point  of  special  interest  is  the  gradual  diminution  of  humus 
percentage  downward  in  each  of  the  composite  columns,  with  an  occa- 
sional slight  increase,  as  is  seen  in  the  eleventh  foot  of  the  Sacramento 
Valley  and  the  twelfth  foot  of  the  Coast  Range  valleys.  This  decrease 
indicates  smaller  amounts  of  humus-forming  vegetable  material,  pre- 
sumably the  roots  of  plants,  in  each  successive  foot  downwards,  the 
main  mass  of  the  root  systems  being  in  the  upper  three  or  four  feet.  . 

Average  of  Three  Upper  Feet.  A  depth  of  one  foot  does  not  in  reality 
represent  a  soil  in  this  State  which  is  at  least  three  feet  deep,  and  it 
would  not  be  correct  or  fair  to  the  cultural  possibilities  of  the  land  to 
draw  conclusions  from  the  humus  of  the  first  foot  alone.  It  is  very 
true  that  its  presence  to  the  extent  of  several  per  cent  near  the  surface 
is  of  special  importance  in  maintaining  proper  physical  textural  con- 
ditions for  aeration,  avoidance  of  crusts  and  easy  penetration  of  water, 
but  it  is  of  as  great  importance  that  there  should  be  several  per  cent 
of  humus  in  each  of  the  upper  several  feet,  for  in  arid  regions  it  is  below 
the  first  foot  and  away  from  hot  and  dry  top  soil  that  the  feeding  roots 
of  plants  prefer  to  carry  on  their  activities,  and  it  is  in  the  upper  three 
feet  that  the  main  mass  of  fine  feeding  roots  is  usually  located,  and 
where  they  must  secure  the  needed  plant  food  supplied  by  the  humus. 
This  not  only  protects  the  roots,  but  gives  to  them  a  far  greater  feeding 
area,  which  is  enlarged  with  the  extension  of  the  humus  downward. 
The  summations  for  three  feet  are  given  at  the  foot  of  the  table. 

Sacramento  Valley.  The  Sacramento  Valley  represented  in  the 
above  table  by  a  composite  column  of  eighteen  individual  columns  is  not 
only  richer  than  the  San  Joaquin  Valley  in  the  first  foot  in  humus,  but 
in  every  foot  of  the  entire  column  to  a  depth  of  twelve  feet.  One  half 
of  the  total  amount  is  held  in  the  upper  three  feet.  Its  first  foot  con- 
tains a  little  less  than  that  of  the  Southern  California  column,  but  in  the 
upper  three  feet  and  in  the  entire  column  there  is  more.  The  percent- 
age in  the  first  foot  is  too  small  and  clearly  shows  the  need  of  its  being 
increased  by  a  system  of  growing  and  turning  under  of  green  crops. 
With  this  to  encourage  the  growth  of  the  young  grain  and  trees  the 
lower  portion  of  the  column  will  afford  humus  nitrogen  and  other  plant 
food  for  the  roots  that  find  their  way  downward  to  twelve  or  more  feet, 
as  was  the  case  with  wheat  and  barley  roots  on  the  University  farm  at 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  85 

Davis.  In  the  latter  soil  the  humus  of  the  first  foot  was  only  .85  per 
cent  and  that  of  the  second  foot'  1.49  per  cent ;  the  ordinary  yield 
had  been  but  from  12  to  14  bushels  of  wheat  per  acre  before  the  Uni- 
versity bought  the  property.  .  By  proper  method  of  treatment  and 
without  irrigation  or  fertilization  the  agronomist  in  charge,  Prof.  G.  W. 
Shaw,  secured  a  yield  of  40.4  bushels  of  wheat  per  acre  as  an  average 
of  three  years,  during  which  time  the  average  for  the  State  was  but 
14.5  bushels.     (Bulletin  No.  211.) 

The  humus-nitrogen  content  of  the  upper  three  feet  of  the  Sacra- 
mento composite  column  is  5.79  per  cent  of  the  humus  and  .04  of  the 
soil.  This  is  approximately  1,600  pounds  of  nitrogen  per  acre  for  each 
foot  in  depth. 

San  Joaquin  Valley.  The  composite  of  23  columns  from  the  San 
Joaquin  Valley  show  humus  percentages  much  below  those  of  other 
regions  both  in  the  surface  foot  (.80  per  cent)  and  in  each  foot  of  the 
entire  column.  The  sum  of  2.91  per  cent,  if  contained  in  the  upper 
foot  of  the  three  feet  would  be  a  fair  amount,  though  much  below  that 
of  other  regions.  The  low  percentages  may  be  due  in  part  to  the 
presence  of  alkali  salts  in  some  of  the  soils  examined,  also  to  a  more 
arid  climate  of  far  less  rainfall  than  in  other  regions,  and  to  a  less 
luxuriant  vegetation  upon  the  decay  of  whose  roots  the  amount  of 
humus  is  dependent. 

Although  this  humus  percentage  is  so  low  in  the  upper  part  of  the 
soil,  yet  a  proper  system  of  deep  plowing  to  break  up  any  tendency  to 
form  a  plowsole  and  to  make  the  soil  loose  and  of  good  texture  for  a 
downward  development  of  the  crop  roots,  which  may  thus  secure  the 
benefits  of  the  humus,  would  tend  to  greatly  increase  the  grain  yields 
of  the  valley.  This  was  shown  in  the  experiments  of  Prof.  G.  W.  Shaw 
at  Ceres  and  Tulare,*  where,  during  a  period  of  three  years  by  this 
method  the  average  yield  of  wheat  was  35  and  33  bushels  respectively, 
while  the  average  wheat  yield  for  the  State  was  14.5  bushels  per  acre. 
No  irrigation  or  fertilization  was  used  in  his  experiments. 

The  humus-nitrogen  of  the  upper  three  feet  of  the  composite  column 
is  6.27  per  cent  of  the  humus,  which  is  higher  than  in  any  of  the  other 
composite  columns  in  the  table.  In  the  soil  itself,  however,  there  is  but 
an  average  of  .04  per  cent  or  1,600  pounds  per  acre  foot. 

Sierra  Nevada  Foothills.  The  composite  of  three  columns  from  the 
Sierra  Nevada  Foothills  shows  more  humus  in  the  first  foot  than  in  that 
of  the  Sacramento  Valley  or  Southern  California.  That  of  the  second 
foot  is,  however,  somewhat  less  and  there  is  a  greater  decrease  in  the 
lower  part  of  the  column,  the  sum  being  but  3.39  per  cent  in  the  eight 
feet.    More  than  one  half  of  the  humus  is  held  in  the  upper  three  feet. 


■Bulletin  No.  211. 


86  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

The  humus-nitrogen  in  the  upper  three  feet  of  the  composite  column 
is  5.40  per  cent  of  the  humus  or  .05  per  cent  in  each  foot  of  the  soil,  and 
is  equivalent  to  2,000  pounds  for  each  acre  foot  in  the  three  feet. 

Coast  Range  Valleys.  The  composite  column  of  the  24  soils  of  the 
valleys  of  the  Coast  Range  shows  a  general  average  of  nearly  two  per 
cent  of  humus  in  the  surface  foot,  and  thus  is  far  above  each  of  the  other 
columns,  except  the  marshes  and  meadow  lands.  Not  only  that,  but  it 
is  the  only  column  of  the  uplands  which  has  more  than  one  per  cent  in 
the  soils  immediately  below  the  first  foot.  The  percentage  of  humus 
in  each  of  the  succeeding  feet  throughout  the  twelve  feet  is  also  higher 
than  in  any  other  of  the  composite  columns ;  the  twelfth  foot  has  nearly 
one  half  of  one  per  cent  and  the  sum  of  the  entire  column  is  9.38  per 
cent.  The  humus  is  not  as  rich  in  nitrogen  as  that  of  the  San  Joaquin 
or  Southern  California,  and  the  amount  of  organic  nitrogen  in  the  soil 
is  below  the  .05  per  cent  regarded  as  necessary  for  fertility. 

Southern  California.  The  soils  of  the  valleys  of  Southern  California 
represented  by  the  composite  of  twenty-five  columns  have  about  the 
same  humus  content  in  the  first  foot,  and  in  the  upper  three  feet,  as  was 
found  in  similar  parts  of  the  columns  from  the  Sacramento  Valley  and 
the  Foothills;  but  is  far  behind  that  of  the  Coast  Range  valleys.  The 
humus  is  well  distributed  downward  to  twelve  feet,  and,  as  with  the 
Sacramento  Valley  soils,  affords  an  excellent  and  large  feeding  area  for 
plant  roots.  Every  encouragement  should  be  given  crops  to  take  advan- 
tage of  this  by  sending  their  roots  deep  into  this  fertile  soil  mass.  The 
upper  three  feet  contain  a  little  less  than  one  half  of  the  total  humus. 

The  humus  of  the  first  foot  is  too  low  for  the  maintenance  of  good 
physical  condition  and  careful  attention  should,  as  a  rule,  be  given  to 
the  turning  under  of  green  crops  and  the  humification  of  the  same. 

The  humus  in  the  upper  three  feet  contains  5.74  per  cent  of  nitrogen, 
but  there  is  only  .03  per  cent  of  organic  nitrogen  in  the  soil:  this  is 
equivalent  to  about  1,200  pounds  per  acre  foot,  which,  under  the 
influence  of  bacteria,  gradually  becomes  available  for  plants. 

"Desert"  Plains.  The  "Desert"  lands  represented  by  a  composite 
of  five  columns  from  the  valleys  of  Imperial,  Coachella,  Owens  River 
and  Mojave  River  are  very  low  in  humus  in  their  upper  several  feet,  as 
is  to  be  expected  from  the  meagerness  of  the  natural  humus-forming 
vegetation.  One  half  of  the  humus  is  held  in  the  upper  five  feet  instead 
of  in  three  as  is  the  case  with  other  regions.  The  presence  of  so  much 
humus  in  the  twelfth  foot  is  a  matter  of  some  surprise,  for  the  lands 
seem  usually  quite  deficient  in  natural  moisture  other  than  hygroscopic 
for  hundreds  of  feet  in  depth.  The  amount  of  humus  in  the  twelfth 
foot  is  one  half  that  of  the  first  foot. 

The  humus  of  the  upper  three  feet  contains  but  4.97  per  cent  of  nitro- 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  87 

gen,  and  there  is  but  .01  per  cent  of  organic  nitrogen  in  the  soil:  this  is 
equivalent  to  about  four  hundred  pounds  per  acre  foot,  which  is  very 
low. 

Lava-bed  Valleys.  The  valley  lands  of  the  lava-bed  region  of  the 
northeastern  part  of  the  State  have  in  the  composite  of  eight  columns  a 
high  percentage  of  humus,  not  only  in  the  first  foot  but  in  the  second. 
This  is  natural,  as  the  soils  are  moist  from  underlying  water  and  there 
is  a  strong  vegetation  whose  roots  penetrate  deeply.  The  total  sum  of 
humus  percentages  in  the  12  feet  is  4.25  per  cent,  the  upper  three  feet 
holding  more  than  one  half  of  it.  The  humus  is  poorer  in  nitrogen  than 
in  any  of  the  regions  except  the  desert,  the  average  in  the  upper  three 
feet  being  3.79  per  cent,  or  .05  per  cent  in  the  soil. 

Tide  Marshes.  The  tule  marshes  near  Stockton  and  Klamath,  and 
the  Pomona  cienega  have  extremely  high  humus  percentages  in  each 
of  the  four  upper  feet,  and  the  humus  is  also  quite  high  through  the 
column  of  eight  feet,  all  derived  from  the  large  amount  of  decaying 
tule  roots.  The  humus  nitrogen  of  the  upper  three  feet  is,  however, 
onty  5.75  per  cent  in  the  humus  or  .44  per  cent  in  the  soil;  the  latter 
is  much  higher  than  found  in  any  of  the  columns. 

Nitrogen   in  the   Humus. 

Nearly  one  thousand  determinations  of  nitrogen  were  made  in  this 
investigation,  and  of  these  there  were  but  64  where  the  humus  was 
found  to  contain  more  than  10  per  cent  of  nitrogen;  fourteen  of  these 
had  from  15  to  20  per  cent  and  but  five  had  more  than  20  per  cent.  The 
latter  percentage  was  found  in  the  eighth  foot  of  the  Berkeley  adobe,  the 
fourth  foot  of  Watsonville  Heights  loam,  the  sixth  foot  of  the  Kenwood 
loam,  the  sixth  foot  of  Santa  Paula  loam,  and  the  fifth  foot  of  the 
Fullerton  loam. 

The  general  average  for  all  of  the  soils,  including  the  marsh  lands,  is 
5.92  per  cent  for  the  first  foot,  5.60  per  cent  for  the  upper  three  feet 
and  5.57  per  cent  for  the  entire  depth  of  twelve  feet. 

The  humus  of  the  surface  foot  of  the  composite  of  Southern  Cali- 
fornia soils  is  richer  in  nitrogen  than  that  of  any  of  the  other  regions 
though  nearly  equaled  by  that  of  the  tule  marshes.  That  of  the  lava- 
bed  valleys  is  poorer  in  nitrogen  than  any  others. 

The  humus  of  the  upper  three  feet  of  the  composite  column  of  the 
San  Joaquin  Valley  is  much  the  richest  in  nitrogen,  and  that  of  the 
lava-beds  again  the  poorest.  Four  of  the  eight  columns  fall  below  the 
general  average  for  the  State.  The  same  is  true  for  the  averages  of 
the  twelve  foot  columns. 

The  differences  in  the  percentages  of  nitrogen  in  the  humus  of  the 
upper  three  feet  and  of  the  total  columns  are  not  very  great,  except  in 
the  valleys  of  the  Coast  Range,  where  it  is  considerably  smaller ;  and  in 


88  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

the  lava  beds  and  "Desert"  plains  where  there  is  a  very  material  fall- 
ing-off. 

Organic   Nitrogen    in   the   Soil. 

It  is  well  to  remark  here  that  .10  per  cent  of  nitrogen  in  the  upper 
foot  of  a  humid  soil  is  regarded  as  an  ample  supply  for  fertility,  while 
in  the  arid  region  with  its  deeper  soil,  deeper  humus  and  deeper  root 
penetration,  one  half  that  amount,  or  .05  per  cent  in  each  of  the  three 
upper  feet  is  considered  sufficient  for  many  years,  because  the  roots 
are  in  a  larger  feeding  area  than  in  the  humid  region,  and  bacterial 
activity  is  greater  and  deeper.  This  percentage  would  mean  2,000 
pounds  of  nitrogen  per  acre  in  each  foot. 

The  marsh  or  tule  soils  of  the  State  have  very  high  amounts  of  nitro- 
gen, as  shown  in  the  Stockton  tule  .83  per  cent,  Klamath  tule  .34  per 
cent  and  the  Pomona  cienega  .25  per  cent,  and  is  probably  due  to  their 
wet,  soggy  condition  and  lack  of  aeration.  This  nitrogen  is,  however, 
less  available  than  that  of  the  dry  uplands,  hence  a  comparison  can  not 
be  made.  The  surface  soils  that  are  richest  in  nitrogen  are,  the  two  soils 
from  the  Arroyo  Grande  Valley,  including  the  Routzahn  Seed  Farm 
with  their  .16  per  cent  of  nitrogen  each,  Gilroy  with  .15  per  cent,  Ber- 
keley and  Farmington  each  with  .14  per  cent,  Burpee  Seed  Farm  of 
Lompoc,  Vaca  Valley,  and  Kenwood  each  with  .13  per  cent,  and  El 
Verano,  Santa  Maria,  Chico,  Yountville,  and  Chino  each  with  .11  per 
cent.    Newcastle  soil  has  .10  per  cent,  while  all  others  have  less. 

Nine  of  the  soils  have  but  .01  per  cent  of  humus-nitrogen  in  the  first 
foot,  seven  have  but  .02,  forty-six  or  nearly  half  of  the  columns  have 
less  than  .05  per  cent,  and  hence  are  much  below  the  desirable  per- 
centage of  nitrogen.  The  average  of  the  first  foot  of  all  of  the  columns, 
excepting  the  marshes,  is  about  .05  per  cent. 

Some  of  the  upland  soils  are  quite  rich  in  organic  nitrogen  in  the 
upper  three  feet,  the  true  soil  mass  of  the  arid  region.  The  adobe  of 
Berkeley  is  the  richest  with  its  .13  per  cent  or  approximately  15,000 
pounds  per  acre  in  a  depth  of  three  feet.  Eight  columns  have  averages 
of  .10  and  upward,  viz,  the  two  Arroyo  Grande  soils,  Gilroy,  Chico, 
Farmington,  Kenwood,  Newcastle,  and  Cottonwood.  Thirty-one 
colums  have  averages  of  from  .06  to  .10  per  cent,  all  others  being  below 
this  amount.  In  other  words,  we  find  that  more  than  half  of  the 
columns  have  in  their  upper  three  feet  less  than  the  .05  per  cent  of 
organic  nitrogen  which  is  considered  necessary  for  fertility.  Many 
have  but  little  more  than  traces  of  the  same. 

In  the  entire  columns  of  twelve  feet  Ave  find  that  there  are  eleven  up- 
land localities  that  have  averages  of  as  much  as  .05  per  cent,  and  among 
these,  Berkeley  and  Arroyo  Grande  columns  stand  highest,  with  averages 
of  .08  per  cent  or  approximately  38,000  pounds  of  organic  nitrogen 
distributed  through  the  depth  of  twelve  feet. 


Bulletin  242] 


HUMUS   IN   CALIFORNIA   SOILS. 


89 


Humus-phosphate   in  the  Soil. 

When  vegetable  matter  is  humified  in  the  soil  the  phosphoric  acid  of 
the  plant  remains  in  combination  in  the  humus  and  that  of  the  soil  is 
also  attacked :  this  humic  phosphoric  acid  is  considered  as  more  avail- 
able to  plants  than  that  in  the  soil.  It  is  probable  that  all  humus  con- 
tains phosphoric  acid,  but  the  amount  varies  very  greatly ;  in  some  soils 
the  percentage  of  humus-phosphate  is  quite  large  and  adds  greatly  to 
the  fertility  of  the  soil.  In  seven  of  the  soil  columns  of  the  State  the 
percentage  of  humus-phosphate  in  the  soil  was  ascertained  through  the 
entire  column,  but  the  chief  interest  lies  in  the  amount  contained  in 
the  upper  three  feet,  the  range  of  annual  plant  roots.  These  results 
are  given  in  the  following  table: 


Phos- 
phoric 
acid  in 

soil, 
per  cent 

In  surface  foot 

In  upper  3  feet 

Humus, 
per  cent 

Humic  phosphoric 
acid 

Humus, 
per  cent 

Humic  phosphoric 
acid 

Per  cent 

Pounds 
per  acre 

Per  cent 

Pounds 
per  acre 

Yuba  City  clay  loam 

Chico   alluvial  soil 

.18 
.09 
.06 
.11 
.18 
.12 
.12 

1.27 
1.84 
1.16 
.37 
1.30 
4.43 
1.23 

.05 

.05 
.05 
.01 

.07 
.07 
.07 

2,000 
2,000 
2,000 
400 
2,800 
2,800- 
2,800 

.93 
1.39 
.81 
.28 
1.25 
3.63 
1.04 

.04 
.      .04 
.03 
.01 
.08 
.04 
.06 

4,800 
4,800 

Stockton  adobe  clay 

Modesto  sandy  soil 

Russian  River  alluvium 

Santa  Clara  adobe  clay___ 
Santa  Paula  clay  loam 

3,600 
1,200 
9,600 
4,800 
7,200 

The  Russian  River  alluvium  and  the  Santa  Paula  clay  loam  are  quite 
high  in  their  percentages  of  humic  phosphoric  acid  in  the  upper  three 
feet;  they  approximate  3,200  and  2,400  pounds  per  acre  for  each  foot 
in  depth ;  an  amount  amply  sufficient  to  supply  the  needs  of  crops  for 
many  years.  In  the  upper  six  feet  of  soil  the  Santa  Paula,  Santa  Clara 
and  Russian  River  columns  have  each  .05  per  cent,  or  approximately 
2,000  pounds  of  immediately  available  phosphoric  acid  in  each  foot. 

These  high  percentages  of  humic  phosphoric  acid,  with  corresponding 
percentages  of  humic  potash  and  humic  nitrogen  throughout  these 
depths  of  twelve  feet  are  strong  reasons  why  deep-rooting  of  plants  and 
trees  should  be  encouraged  by  a  deep  water  supply  and  deep  cultivation 
or  plowing. 

Comparison  of  Arid  and  Humid  Soils. 

A  comparison  between  the  soils  of  the  arid  and  humid  regions  brings 
out  the  very  great  advantages  possessed  by  the  former,  and  especially 
by  those  of  California,  over  the  humid,  as  shown  in  the  first  part  of  this 
bulletin.  But  it  is  especially  marked  in  the  amount  and  distribution 
of  humus  in  the  soils  of  the  respective  regions.* 


*It  has  been  a  rather  difficult  matter  to  secure  data  on  humus  in  the  soils  east  of 
the  Mississippi  River  for  the  reason  that  in  their  analyses  some  of  the  chemists  have 
failed  to  separate  it  from  the  percentage  of  aggregate  "organic  matter." 


90 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


The  general  average  in  280  soils  of  the  humid  portion  of  the  United 
States  is  2.63  per  cent,  and  if  we  add  to  this  the  5.26  per  cent  in  eleven 
tropical  soils  of  Hawaii,  the  average  is  brought  to  2.73  per  cent  or 
approximately  109,200  pounds  per  acre. 

The  average  of  the  331  California  soils  and  44  from  Idaho,  Arizona, 
and  Oregon  is  1.28  per  cent  for  the  surface  foot,  or  less  than  one  half 
that  of  the  humid  region.  For  the  first  foot  of  the  109  soil  columns  the 
average  is  1.35  per  cent. 

But  the  depth  of  soil  in  which  most  of  the  plant  roots  are  held  and  in 
which  the  humus  color  is  most  pronounced  is  three  feet,  and  taking 
this  as  the  true  soil  of  California  we  find  that  there  is  a  sum  of  3.17  per 
cent,  or  an  average  of  1.06  for  each  foot;  this  is  equivalent  to  about 
126,800  pounds  per  acre.  To  this  should  be  added  the  percentages  of 
humus  found  at  lower  levels  of  the  soil,  as  shown  in  the  averages  of  the 
109  columns  given  in  the  accompanying  table,  which  would  bring  the 
total  humus  to  234,000  pounds  in  12  feet. 

Average  of  Humus  in 


Arid  soils 

109  California 

soil  columns. 

per  cent 

342  soils. 

general,  per 

cent 

291  soils. 

general,  per 

cent 

1-foot  soil  

2-foot  soil  

3-foot  soil  

4-foot  subsoil  

5-foot  subsoil  

6-foot  subsoil  __  _  _ _. 

1.35 

1.04 

.78 

.62 

.45 

.36 

.30 

.26 

.21 

.18 

.14 

.14 

5.83 

3.17 

5.60 

.05 

1.28 

9 

2.73 
? 

7-foot  subsoil  ________    _  _  _  _. 

8-foot  subsoil  

9-foot  subsoil 

10-foot  subsoil 

11-foot  subsoil 

12-foot  subsoil    _  _ 

Sum  of  per  cents  in  12  feet 

Sum  of  per  cents  in  3  feet__    __  _      _  _  _  _ 

Nitrogen  in  humus,  3  feet  _____        _    _ 

Nitrogen  in  soil,  3  feet _. 

The  amount  of  humus  then  in  the  average  of  California  soils  (3  feet 
deep )  is  greater  than  in  those  of  the  humid  region ;  and  for  the  depth 
of  twelve  feet  it  is  more  than  twice  as  great. 

The  determinations  of  humus-nitrogen  in  the  soils  of  the  humid 
region  have  been  so  few  and  miscellaneous  that  it  is  not  advisable  to 
deduce  from  them  an  average  to  represent  the  whole  region. 

Arid  California  with  her  deep  soils  of  well  diffused  humus  and  rich- 
ness in  plant  food  thus  possesses  very  great  advantages  over  the  more 
humid  East,  where  a  depth  of  six  to  nine  inches  is  very  generally 
acepted  as  that  of  a  true  upland  surface  soil,  containing  practically  all 
of  the  humus  and  marked  by  a  very  sharp  change  of  the  black  humus 
color  to  the  gray  and  yellow  subsoil  with  its  inappreciable  amount  of 


Bulletin  242]  HUMUS   IN    CALIFORNIA   SOILS.  91 

humus.*     In  the  sediment  lands  of  the  streams  and  some  of  the  black 
prairies  the  humus  is  of  course  found  at  a  greater  depth. 

CONCLUSIONS. 

1.  The  depth  of  the  soils  of  California  is  indefinite  because  of  the 
presence  of  humus  to  and  beyond  twelve  feet  below  the  surface.  The 
upper  three  feet  may,  however,  properly  be  called  the  soil,  for  within 
that  depth  the  greater  part  of  the  feeding  roots  of  plants  are  found. 
The  sharply  denned  change  of  the  black  humus  color  to  gray  at  6  or  9 
inches  that  marks  the  depth  of  humid  soils,  is  present  in  some  of  the 
heavy  clay  soils  in  California  at  the  depth  of  three  feet  ;•  but  for  the 
most  part  the  change  in  tint  is  very  gradual  downward  through  many 
feet. 

2.  The  soils  of  California  are  richer  in  humus  than  has  generally 
been  supposed;  in  their  depth  of  three  feet  (the  soil  proper)  they 
contain  more  than  in  the  humid  soils,  and  in  the  entire  columns  of 
twelve  feet  or  more  they  have  double  that  of  the  humid  soils. 

3.  The  humus  in  California  soils  is  usually  distributed  through 
depths  of  twelve  or  more  feet,  the  highest  percentage  being  in  the  upper 
three  feet  and  diminishing  downward,  as  shown  in  each  of  the  109  soil 
columns  taken  from  the  several  agricultural  regions ;  as  much  as  .41 
per  cent  was  found  in  the  fifteenth  foot  of  the  Fort  Romie  column,  and 
.74  per  cent  in  the  thirteenth  foot  of  that  of  Davis  and  Hayward ;  water 
was  reached  in  each  case. 

4  The  surface  soils  of  California  have  an  average  of  1.28  per  cent  of 
humus,  as  shown  in  the  analysis  of  several  hundred  samples  taken  from 
the  many  agricultural  regions  of  the  State.  This  is  not  sufficient  to 
maintain  good  tilth  in  the  soil;  but  as  supplemented  by  that  of  many 
feet  below,  often  affords  a  fair  supply  of  nitrogen.  The  upper  three 
feet  of  soil  proper  have  an  average  of  1.06  per  cent  per  foot,  or  a  sum 
of  3.17  per  cent. 

5.  The  tule  swamps  have  the  highest  percentage  of  humus  because  of 
the  mass  of  decaying  roots  and  other  vegetable  matter,  while  the  deserts 
have  the  least. 

6.  Humification  is  retarded  in  close  compact  adobe  clays,  and  the 
amount  of  humus  is  less  than  in  lighter  loam  and  sandy  soils. 

7.  The  valleys  of  the  Coast  Range  in  the  western  part  of  the  State 
have  higher  percentages  of  humus  in  their  soils  than  have  any  of  the 
other  agricultural  regions,  probably  because  of  the  greater  humidity  of 
the  climate  of  that  region,  and  a  denser  vegetation. 


*See  Hilgard's  Soils,  page  164,  and  Agricultural  Science,  1892,  page  263  ;  King's 
The  Soil,  page  29  ;  Hall's  Soils,  page  45  ;  Minn.  Bulletins  30,  41  and  65  contain 
analyses  of  121  subsoils,  in  only  16  of  which  is  humus  reported  though  found  in  all 
of  the  corresponding  surface  soils  which  were  taken  to  depths  of  nine  inches.  (Bul- 
letin  30,  page  164.) 


92  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

8.  Arid  soils  have  an  immense  advantage  over  those  of  the  humid 
region  of  the  United  States  because  of  this  distribution  of  humus  and 
its  nitrogen  through  a  depth  of  many  feet ;  as  it  gives  a  greater  depth  of 
soil  and  induces  a  deeper  root  penetration  for  plants  and  trees  into  a 
greater  feeding  area  and  where  there  is  more  moisture.  The  wonderful 
endurance  of  drought  on  the  part  of  plants  on  California  soils  is  due  to 
this. 

9.  Humus  contains  nitrogen  in  combination,  the  amount  depending 
on  the  source  of  the  humus.  The  average  percentage  in  the  humus  of 
the  first  foot  of  the  soil  columns  is  5.92  per  cent;  that  of  each  of  the 
upper  three 'feet  is  5.60,  and  a  little  less  for  the  entire  twelve  feet  in 
depth.    It  varies  from  one  to  twenty  per  cent  in  individual  soil  layers. 

10.  The  organic  nitrogen  in  the  soil  derived  from  the  humus  and 
dependent  on  the  amount  of  the  latter,  varies  from  almost  nothing  in 
the  lower  depths  of  the  soil  to  as  much  as  .13  in  the  upper  three  feet. 
The  average  for  the  first  foot  of  the  soil  columns  is  .07  per  cent ;  for  each 
of  the  three  upper  feet,  the  range  of  most  annual  plant  roots,  it  is  .05 
per  cent.  The  investigations  of  Professor  Lipman  of  this  station  show 
that  nitrifying  bacteria  are  present  and  active  in  California  soils  to  a 
depth  of  six  feet,  and  ammonifying  bacteria  are  present  through  a  depth 
of  twelve  feet ;  thus  making  available  to  plants  the  nitrogen  content  of 
the  humus  to  these  depths. 

11.  The  humus  of  the  soils  of  this  State  is  very  generally  derived 
from  plant  roots,  instead  of  from  accumulations  of  vegetable  material 
at  various  depths  as  the  soil  wTas  being  built  up;  thus  showing  that 
these  plants  have  for  ages  been  deep-rooted. 

12.  The  black  color  of  a  soil  is  not  always  due  to  a  high  humus  con- 
tent ;  many  black  soils  have  a  smaller  percentage  of  humus  than  soils  of 
a  gray  color.  In  one  instance  a  very  black  clay  soil  from  the  Santa 
Clara  Valley  contained  no  humus,  its  color  being  due  to  the  presence  of 
a  black  mineral. 

13.  Humus  contains  soluble  mineral  plant  food  in  combination,  the 
phosphoric  acid  being  present  in  the  humus  of  California  soils  to  the 
extent  of  from  .01  per  cent  to  .08  per  cent  throughout  the  entire  depth 
to  which  humus  reaches,  though  usually  greatest  in  the  upper  few  feet. 

14.  Humus  is  sometimes  less  in  the  first  foot  than  in  the  second, 
because  it  is  gradually  destroyed  by  cultivation  and  summer-fallowing 
of  the  soil;  but  may  be  replaced  and  increased  by  proper  methods  of 
green-manuring,  or  the  turning  under  and  humification  of  green  crops, 
preferably  legumes. 


TABLE  OF  CONTENTS. 

Page. 
Nature  of  Humus;  amount  formed  from  vegetable  matter 49 

Value  of  Humus  ;  improves  soil  texture ;   prevents  crusting  of  surface  ;  absorbs 
water;  promotes  chemical  activity;  a  nitrogen  fertilizer;  and  contains  mineral 

plant    food    50 

Destruction  of  Humus 54 

Humus  in  California  Soils 54 

Humus  in  the  surface  foot 55 

Cursory  examination  of  soils  received  from  farmers 56 

Accurate  analyses  of  selected  soils 56 

Distribution  of  Humus  downward  in  soils;  bacterial  activity;  leveling  of  lands_  58 

Distribution  of  Humus  in   Soil   Columns  from  each  Agricultural   region 60 

Sacramento  Valley  ;  18  soil  columns. 

Alluvial  lands  ;  Dark  valley  loams  ;  Black  adobe  soils  ;  Red  mesa  and 
bed-rock    lands    60 

San  Joaquin  Valley  ;  24  soil  columns. 

River  alluvial  lands  and  Tule  marshes ;  Black  adobe  clays ;  Reddish 
clay  lands ;  Delta  plains  of  Kings  and  Kern  rivers ;  Gray  sandy 
loams  and  sandy  soils  ;  Gray  clay  loams  ;  Gray  alkali  soils ;  Tulare 
lake    bed    62 

Lower  Foothills  of  Sierra  Nevada ;  3  soil  columns. 

Palermo,   Newcastle  and   Jackson   67 

Coast  Range  Valleys ;  24  soil  columns. 

Russian  River  Valley ;  Santa  Rosa  Valley ;  Los  Guillocos  Valley ; 
Sonoma  Valley ;  Napa  Valley ;  Vaca  Valley ;  Alameda  Plains ; 
Ignacio  Valley  ;  San  Ramon  Valley ;  Livermore  Valley ;  Santa  Clara 
Valley ;  Pajaro  Valley ;  Salinas  Valley ;  Arroyo  Grande  Valley ; 
Santa  Maria  Valley;  Lompoc  Valley 68 

Southern   California   Region  ;   26  soil  columns. 

Saticoy  Plains  ;  Santa  Clara  River  delta  ;  Pleasant  Valley  hill  slope ; 
San  Fernando  Valley ;  San  Gabriel  Valley  ;  San  Bernardino  Valley, 
lowlands,  and  mesa ;  Los  Angeles  alluvial  plain ;  Fallbrook  mesa ; 
Escondido  Valley;   El  Cajon  Valley 72 

Northeastern  Lava-bed  Region ;  9  soil  columns. 

Honey  Lake  Valley ;  Madaline  Plains ;  Pit  River  Valley ;  Surprise 
Valley;   Klamath  Lake  marsh 77 

Desert  Plains  ;  5  soil  columns. 

Imperial  Valley  ;  Coachella  Valley ;  Mojave  River  mesa ;  Owens  River 
Valley 80 

General  Summary. 

Individual  soils  having  highest  humus  content 82 

Comparison  of  Agricultural  Regions ;   composite  columns 83 

Nitrogen  in  humus  of  the  soil  columns 87 

Nitrogen  in  the  soil 88 

Comparison  of  Humus  in  Arid  and  Humid  soils 89 

Humus   phosphate   in   the  soil 89 

Conclusions :_  91 


